7P Drawing tablets
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  • Basics
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    • Learning digital art
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      • Gaming with a drawing tablet
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      • Using a drawing tablet as a mouse replacement
    • Contacting support
    • Drawing tablets vs mice
    • The drawing experience
    • Uninstalling tablet drivers
  • Buying a drawing tablet
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    • Inspecting a drawing tablet
    • Pen tablets vs pen displays
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    • Buying a drawing tablet for osu!
    • Buying tips
    • How many pressure levels do you really need?
    • Choosing the right size for a drawing tablet
    • Switching from a pen tablet to a pen display
    • Buying a drawing tablet as a gift
  • Recommendations
    • Recommended drawing tablets for beginners
    • Dedicated note taking devices
    • Pen tablet recommendations
      • Small pen tablet recommendations
      • Medium pen tablet recommendations
      • Large pen tablet recommendations
    • Pen display recommendations
      • Small pen display recommendations
      • Medium pen display recommendations
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    • Standalone drawing tablet recommendations
      • Pen computer recommendations
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    • Comparisons
      • 7P: Drawing tablet tier list (December 2024)
      • 7P: Large pen tablets compared
      • 7P: 13" pen displays compared (2023)
      • 7P: 22" pen displays compared (2024)
  • Brands
    • Huion and XP-Pen
    • Wacom
    • Xencelabs
    • Drawing tablet brands vs digitizers
    • Choosing a drawing tablet brand
  • Core features
    • Active area
    • Active area size
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    • Disable pen tilt
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    • Pen pressure
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    • Pen pressure response
    • Pen pressure curve
      • Misc pressure curve notes
      • Pressure curves that constrain output
      • Null pressure curve
      • Implementing pressure curves
      • Pressure curves that ignore input
      • Pressure curve shape support in applications
    • Disable pen pressure
    • Pen hover
    • Pen tracking
    • Pen tilt compensation
    • Pen barrel rotation
    • Pen nib travel
    • Pen nib material
    • Lag
    • Pointer lag
    • Brush lag
    • Diagonal wobble
    • Surface texture
    • Auxiliary inputs
    • Absolute versus relative positioning
    • Mouse mode
    • Powering a pen
    • Powering a drawing tablet
  • Guides
    • Caring for your drawing tablet
      • Dealing with water damage
      • Cleaning a drawing tablet
      • Removing a nib
      • Removing a broken nib
      • Storing your pen
      • Surface wear on pen tablets
      • Scratches on pen tablets
      • Texture erosion on pen tablets
      • Surface wear on pen displays
      • False scratches
      • Removing and replacing the surface film on a pen display
      • Nib wear
      • Replacing a pen
    • Customizing your experience
      • Match aspect ratios with Force Proportions
      • Shrinking the active area
      • Using large pen tablets
      • Using extra-large pen tablets
      • Matching pen tablet size to monitor size
      • Active Area Mapping for pen tablets and widescreen monitors
      • Mirroring or extending your desktop to a pen display
      • Using a pen display as a pen tablet
      • Using metal nibs
      • Clamping wide-gamut displays to sRGB
      • Calibrate pen position on a pen display
      • Using a pen display as a monitor
      • Controlling the pen tip behavior
    • Connections and cabling
      • Connecting a pen display with a 3-in-1 cable
      • Connecting a pen tablet to a computer
      • Wireless connection
      • Motherboard HDMI vs GPU HDMI ports
      • Connecting a pen display to a computer
      • Connecting a pen display to a mobile device
      • Connecting a pen display with a single USB-C cable
      • Using 3rd-party cables with your drawing tablet
        • Cables I use to connect pen tablets
      • Connecting a pen to a drawing tablet
      • Recessed USB-C ports
      • Connecting a pen display to a USB-C port on a GPU
    • Drawing
      • Drawing smooth strokes
      • How a brush engine uses pen data
      • Configure smoothing in applications
      • Enable tilt for brushes
    • Pen displays
      • Etched glass vs film
      • Etched glass
      • Anti-glare film
      • Anti-glare sparkle
      • Lamination
      • Display resolution
      • Choosing the right display resolution for a pen display
      • Brightness
      • Parallax
      • Display connector types
      • Using HDMI splitters with pen displays
      • Using HDMI adapters with pen displays
        • VGA to HDMI adapters
        • DVI to HDMI adapters
        • USB-C to HDMI adapters
        • DisplayPort to HDMI adapters
      • Color tint on edges of display
      • Pen display refresh rate
      • USB-C DisplayPort alt mode
      • Dead pixels
      • Using an iPad with your computer as a pen display
    • Pens
      • Pen buttons
      • Pen compatibility with drawing tablets
      • Pen weight
      • Pen weight comparison
      • Pen teardowns
    • Drivers
      • OpenTabletDriver
        • Install OpenTabletDriver on Windows
        • Install OpenTabletDriver on MacOS
        • OpenTabletDriver application data directory
        • Uninstalling OpenTabletDriver on Windows
        • OpenTabletDriver usage notes
        • Smoothing with OpenTabletDriver
        • Pressure curves in OpenTabletDriver
        • Slimy Scylla
      • Using a drawing tablet without installing drivers
      • Tablet Driver Cleanup tool
      • Using older tablet drivers
      • Importing and Exporting tablet driver configurations
    • Advanced
      • Firmware
      • Tablet reports
      • PenTracker by Patrick Lauke
    • Ergonomics
      • Body posture when using drawing tablets
      • Handedness of drawing tablets
      • Using a drawing tablet in portrait mode
      • Rotating a drawing tablet
      • Using a drawing tablet on your lap
      • Noise
      • Using a drawing tablet in bed
      • Heat
    • Touch support
      • Tablets that support touch
    • General
      • Total cost of ownership (TCO)
      • Model names vs model numbers
      • Finding the model number of a drawing tablet
      • Using older drawing tablets
      • Electromagnetic Interference
      • Connecting a drawing tablet to an iPad or iPhone
      • Connecting a drawing tablet to an Android device
      • Testing Drawing Tablet Compatibility with Android devices
      • Connecting a drawing tablet to a Chromebook
      • Chromebook testing results
      • Connecting multiple drawing tablets at the same time
    • Linux
    • Windows
      • Using a drawing tablet on Windows
      • Windows on ARM
      • Windows PNP support for drawing tablets
      • Windows PNP driver compatibility testing
      • Disable ripple effect rings in Windows
      • Disable the press-and-hold ring in Windows
      • Windows 7 Tablet PC features
        • Disable Tablet PC features on Windows 7
        • Disable Tablet PC features on Windows 7 using the FixMyPen tool
      • Windows Ink
        • The history of Windows Ink
        • Configure Windows Ink for apps
        • Configuring Photoshop to NOT use Windows Ink
        • Configure Windows Ink in the tablet driver
      • Stop using a display on Windows
    • Mini-PCs for digital art
      • 7P: Minisforum Neptune HX99G
    • Laptops for digital art
  • Applications
    • Apps for beginners
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    • List of apps
    • App tips
      • Show document canvas on another display
    • 7P: Recommended apps
  • Developers
    • Pen APIs
    • WinTab versus Windows Ink
    • 7P Tablet Tester
    • WinTab API
    • Force proportions simulator
  • Troubleshooting
    • Common problems with drawing tablets
    • Common drawing troubleshooting steps
    • Testing pressure in the tablet driver
    • Check if pen display shows HDMI video signal from other devices
    • Check tablet driver diagnostics
    • Reset a drawing tablet
    • TSG: Low pressure drawing problems
    • TSG: Difficult to reach maximum pressure
    • Testing with Windows PNP drawing tablet drivers
    • TSG: pointer stuck in corner of screen
    • TSG: Drawing problems
    • TSG: Pen display shows NO SIGNAL message
    • TSG: Pen moving pointer on the wrong display
    • TSG: Pixel noise on display
    • TSG: No pressure while drawing
    • TSG: Random gaps in strokes
    • TSG: Dots at end of strokes
    • TSG: Dots at start of strokes
    • TSG: Pen draws while hovering
    • TSG: Hooks at start of strokes
    • TSG: shoelaces at end of strokes
    • TSG: Straight lines at start of stokes
    • TSG: Pen not drawing in vertical or horizontal bands
    • TSG: WiFi and Internet problems with drawing tablets
    • TSG: Tablet driver does not detect tablet
    • TSG: computer does not detect display
    • TSG: driver no longer supports a drawing tablet
    • TSG: no sound after plugging in drawing tablet
    • TSG: Pen display doesn't show anything
    • TSG: Not enough HDMI ports
    • TSG: Insects in a pen display
    • TSG: Pen acting like a mouse
    • TSG: Pen display turns on and off constantly
    • TSG: computer detects drawing tablet as a keyboard
  • Product links
    • Apple
      • Apple iPad
      • Apple Pencil
      • Connecting an iPad to a computer as a drawing tablet
      • 7P: Apple iPad
      • 7P: Apple iPad versus drawing tablets
      • 7P: Apple iPad versus Samsung Galaxy Tab S
      • 7P: How I use iPads
      • 7P: M3 MacBook Pro
    • Artisul
    • ASUS
      • ASUS Pro Art Pen Display
    • CalDigit
      • 7P: CalDigit USB-C to HDMI 2.1 adapter
      • 7P: CalDigit TS4 Thunderbolt Dock
    • Dell
      • Dell Canvas 27
    • Gaomon
      • Gaomon Pen Tablet
      • Gaomon Pro Pen Tablet
      • Gaomon Pen Display
      • Gaomon Pro Pen Display
    • Huion
      • Huion Kamvas Pro
        • 7P: Huion Kamvas Pro 19 (GT1902)
        • 7P: Huion Kamvas Pro 16 Plus 4K (GT1562)
        • 7P: Huion Kamvas Pro 24 4K (GT2401)
      • Huion Kamvas Studio
      • Huion Kamvas Slate
      • Huion Kamvas
        • 7P: Huion Kamvas 13 GEN3 (GS1333)
        • 7P: Huion Kamvas 16 2021 (GS1562)
        • 7P: Huion Kamvas 13 (GS1331)
        • 7P: Huion Kamvas 22 Plus (GS2202)
        • 7P: Huion Kamvas 16 GEN3 (GS1563)
      • Huion Inspiroy R-series
        • 7P: Huion Inspiroy RTP-700
      • Inspiroy Dial
        • 7P: Huion Inspiroy Dial 2 (Q630M)
      • Huion Inspiroy Frego
        • 7P: Huion Inspiroy Frego M (L610)
      • Huion Inspiroy
        • 7P: Huion Inspiroy Giano (G930L)
        • 7P: Huion Inspiroy HS611
        • 7P: Huion Inspiroy WH1409V2
      • Huion KeyDial
      • Huion pens
        • Huion PenTech
        • 7P: Huion PW500 pen
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        • 7P: Huion PW550 series pens
        • 7P: Huion PW600 series pens
        • 7P: Huion PW507 pen
      • Huion Inspiroy 2
        • 7P: Huion Inspiroy 2 L (H1061P)
    • Microsoft
      • Microsoft Surface Pro
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    • OnePlus
      • OnePlus Pad
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      • Samsung S Pen
        • 7P: Samsung S Pen
    • Wacom
      • 7P: Comparison of Wacom pen tablets
      • Wacom model number format
      • Wacom One vs One by Wacom
      • Wacom tablet list
      • One by Wacom
        • 7P: One by Wacom (CTL-x72)
      • Wacom Intuos Pro 2025
        • 7P: Wacom Intuos Pro 2025 (PTK-x70)
      • Wacom Intuos Pro 2017
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        • 7P: Wacom Intuos Pro 2017 (PTH-x60)
      • Wacom Intuos Pro 2013
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        • 7P: Wacom Intuos 4 XL (PTK-1240)
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      • Wacom Cintiq Pro
        • 7P: Wacom Cintiq Pro 16 (DTH-167)
        • 7P: Cintiq Pro 24 (DTx-2420)
        • 7P: Wacom Cintiq Pro 27 (DTH-271)
        • 7P: Wacom Cintiq Pro 22 (DTH-227)
      • Wacom Movink
        • 7P: Wacom Movink 13 (DTH-135)
      • Wacom One 2019 GEN1
        • 7P: Wacom One 2019 GEN1 (DTC-133)
      • Wacom One 2023 GEN2
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        • 7P: Wacom One 2023 pen tablets
      • Wacom accessories
        • 7P: Wacom Converter (ACK45219Z)
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          • 7P: Wacom 2K Pen (LP-190K)
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          • 7P: Wacom One 2023 Pen (CP-923)
          • 7P: Wacom Pro Pen 3 (ACP-500)
          • 7P: Wacom Intuos 2 Airbrush pen (XP-400E)
        • Wacom pen compatibility
    • Xencelabs
      • Xencelabs Quick Keys
      • 7P: Xencelabs Pen Tablet Medium (BPH1212W-A)
      • 7P: Xencelabs Pen Display 16 (LPH1612U-A)
      • 7P: Xencelabs V2 pens
      • 7P: Xencelabs Mobile Easel
      • 7P: Xencelabs Pen Display 24 (LPH2412U-A)
    • XP-Pen
      • XP-Pen Magic Note Pad (MNP1095)
      • XP-Pen Magic Drawing Pad
      • XP-Pen Artist
        • 7P: XP-Pen Artist 22 Plus (MD220FH)
      • XP-Pen Artist GEN2
        • 7P: XP-Pen Artist 12 Gen2 (CD120FH)
        • 7P: XP-Pen Artist 13 GEN2 (CD130FH)
        • 7P: XP-Pen Artist 16 GEN2 (CD160FH)
      • XP-Pen Artist Pro
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        • 7P: XP-Pen Artist Pro 22 GEN2 (MD220QH)
        • 7P: XP-Pen Artist Pro 19 GEN2 (MD180UH)
        • 7P : XP-Pen Artist Pro 16 GEN2 (MD160QH)
      • XP-Pen Shortcut Remote
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        • 7P: XP-Pen Deco LW (IT1060B)
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        • 7P: XP-Pen Deco Pro XLW GEN2 (MT1592B)
      • XP-Pen Innovator
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        • 7P: XP-Pen X3 Pro pens
        • 7P: XP-Pen X3 Elite pen
      • XP-Pen ACS15 Ergo Stand
    • Ugee
  • Application links
    • MyPaint
    • Adobe Photoshop
      • 7P: Adobe Photoshop
    • ArtRage
    • Affinity Photo
      • 7P: Affinity Photo
    • Autodesk Maya
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      • 7P: Clip Studio Paint
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      • 7P: Krita
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  • Accessories
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        • 7P: TourBox
      • 8bitdo controller
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    • Pen grips
    • Protective cases
    • Surface protectors
      • Foxbox covers
      • Photodon screen protectors
      • ePlastic polycarbonate sheets (velvet lexan)
      • Paperlike for iPad
    • Monitor arms
      • 7P: Ergotron monitor arms
    • Stands
      • 7P: VIVO Pneumatic Arm Monitor Desk Stand (STAND-V100R)
      • Parblo PR-100 stand
        • 7P: Parblo PR-100 Stand
      • XP-Pen AC41/AC42 stands
      • XOOT Stand
      • iPad stands
  • Resources
    • Drawing tablet community
    • Kuuube
      • Kuuube's Wacom tablet mastersheet
      • Kuuube's tablet buying guide
      • Kuuube's Wacom pen compatibility mastersheet
    • YouTube channels
    • Subreddits for drawing tablets
    • Koneko_w
    • Project Patchouli
  • Process
    • Pressure range data
    • Measuring hover height
    • Measuring pressure
    • Measuring display sharpness
    • Measuring report rate
    • Measuring diagonal wobble
    • Diagonal wobble samples
    • Perfect pressure sensitive lines
    • Tablet evaluation
    • Microscope
  • Reference
    • Resolution info
    • Aspect ratio math
    • Standard paper sizes
  • Technology
    • Display panel technology
    • VESA
    • Wacom patents
    • AES
    • Apple Pencil tech
    • EMR
      • EMR technical resources
      • EMR position detection
      • EMR pressure detection
      • Active EMR vs Passive EMR
      • EMR tilt detection
      • The realities of building your own EMR pen
    • MPP
    • Digital pen tech
    • Wacom UD EMR
      • Pens that support UD EMR 2nd gen
      • Tablets that support UD EMR 2nd gen
    • USI
  • Misc
    • Circuit simulations
    • History of drawing tablets
      • Preface
      • Chapter 1: Antiquity
      • Chapter 2: Terms
      • Appendix: Timeline
      • Appendix: Other histories
      • Appendix: References
    • Mobile computer recommendations
Powered by GitBook
On this page
  • Overview
  • The EMR sensor (aka the digitizer)
  • Detecting a signal with a coil
  • An array of coils
  • A grid of coils
  • Basic position detection
  • Interpolation of position
  • Position at the corners and edges
Export as PDF
  1. Technology
  2. EMR

EMR position detection

Last updated 11 months ago

Overview

The starting point for understanding EMR is learning how the tablet detects the position of the pen. Once this is known, many other aspects of the tablet can be understand.

The tablet and pen are communicating with each other. They swap between listening and transmitting an electromagnetic signal many times a second. This document focuses on the pen producing an electromagnetic signal that the tablet detects.

Please keep in mind, this is a simplified, conceptual explanation. Naturally, the description leaves out many details.

The EMR sensor (aka the digitizer)

The fundamental component of a drawing tablet the EMR sensor. The more common name for this is digitizer.

The digitizer is a printed circuit board (PCB) that contains:

  • Some chips

  • Some firmware code running in some of this chips

  • a set of coils (wires) laid out on the PCB. The coils that are laid out vertically are clearly visible. The horizontal coils are partially visible as darker regions on the green PCB.

This is the top of the Wacom digitizer used in the Wacom Intuos Pen Small (CTL-480). This is a smaller version of a on Wikipedia commons.

The digitizer has something underneath it (on top on the photo) - this is probably a thin piece of something metallic to prevent electromagnetic interference from this device to others from the bottom of the tablet.

In this view you can see chips on the digitizer PCB attached to other components inside the tablet.

Now that we know what the digitizer looks like, by exploring position detection, we can understand what we are seeing.

Detecting a signal with a coil

The coil is a piece of wire that extends from a digitizer chip.

NOTE:

  • A real digitizer will have multiple chips, but in these diagrams only 1 or 2 chips are shown.

  • The wire does not look like what you might think of as a "coil". If you look up an electromagnetic component called an "inductor" you'll realize why it has this name. Another doc covering the LC Circuit in EMR pens will explain it in more detail.

If the pen is sending an electromagnetic signal and is near the coil. The signal will induce a current in the coil. This is called electromagnetic induction - meaning a current in one thing is causing a current in something else even though they are not touching. The chip registers the strength of this signal - I draw it as a light blue bar near the detector. The closer the pen is the stronger the signal. If the pen is far enough away, there really isn't any current detected on the coil.

Key points

  • At this stage, the signal on the coil tells us something about how far away the pen is, but nothing else.

  • The coil is oriented vertically but it doesn't know the vertical position of the pen. The pen could be on the top or the middle or near the bottom and the coil wouldn't know it.

An array of coils

Lets have multiple coils next to each other in a row horizontally. Each coil independently detects the signal from the pen. So the signal strength is different for each coil - and depends on how far away the pen is from that specific coil.

The pen is right on top of one coil so it has the strongest signal. As coils are further from the pen the strength diminishes. And of course some coils essentially don't detect any signal.

The coils are going up and down, but the set of coils are arranged horizontally. This arrangement means that the coils can detect the horizontal location of the pen, but again the coils have now idea were the pen is vertically.

A grid of coils

Before we continue, I'm going to draw the coils in a simpler way. It will look like I am drawing them as a wire just sticking out of the detector, but really think of them as looping back into the detector. Drawing it this way will make looking at the later diagrams a bit easier.

Now we are going to have two arrays of coils. One is a horizontal array like we had above. But the other array is oriented vertically.

Now we are going but these arrays on top of each other.

I must stress this, even the diagram makes it look like the horizontal and vertical coils are touching - they are not touching at all. They are on two separate layers. None of the coils actually touch another coil.

Basic position detection

With the coils arranged horizontally and vertically, the coils can detect the position of the pen. Th e vertical coils detect the horizontal (x) position. The horizontal coils detect the vertical (y) position.

Again notice that multiple coils in each dimension are detecting the signal for the pen.

In this diagram below, the pen coincidentally is right on top of one vertical coil and one horizontal coil. As a result, a single strong peak signal for the both the horizontal and vertical components.

Interpolation of position

Drawing tablets do not have a large number of coils. Not thousands. Not hundreds. They have more like tens of coils for each of the horizontal and vertical dimensions.

The consequence of this very sparse arrangement of coils is that the vast majority of the time, the pen is NOT exactly on top of a specific coil. It's almost always between two coils.

Also only a small number of coils detect the pen. For example in in any given dimension it could be only 4 coils that detect the pen.

In this case above the pen is exactly in-between two horizontal coils and exactly in-between two vertical coils. So now in both the horizontal and vertical directions, there isn't a single strong signal, two signals in each direction have the same value. So the tablet, can infer that the pen is exactly between coils in both directions.

And of course the pen may not not be exactly on or exactly in-between coils as shown below.

So, a drawing tablet has to carefully look at the signal strengths to handle all these cases of the pen's position. Fortunately EMR tablets are very fast and accurate at doing this. In terms of resolution, a typical Wacom EMR tablet can identify 5080 different positions inside every inch - that's 200 different positions for every millimeter! As you can see, the resolution of detection is surprisingly good.

Position at the corners and edges

When the pen is in the middle of the tablet, there are lots of coils that detect the pen.

But the pen can also be at the edge or corner of the grid of coils. In this case there are fewer coils detecting the pen.

With fewer coils detecting the pen in this scenario the tablet has less data to work with to estimate the position of the pen. You will notice this in almost all tablets - that as you get within about 3mm of the edges or corners the pointer will start to drift away from the tip of the pen.

This loss of accuracy is typical and is present in all tablets - even the most high-end professional ones.

Tablet manufacturers try to counteract this a little bit. The surface of the tablet will usually mark out the corners of the active area.

We represent the active area as a red box in this diagrams, you'll notice that the active area is not the full size of the grid. Instead it is inset a little bit. This helps the tablet identify the pens position at what you see as the active area.

The bottom of the digitizer is below. You can see the .

larger version here
much larger image