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Testing the Accuracy of Pen Tablets
INTRODUCTIONMovAlyzeR® movement analysis software enables users to estimate the accuracy of a pen tablet. Pen tablets can be evaluated mainly by spatial and temporal errors. A brief overview of what is tested is below, followed by the test procedure. Links to actual accuracy tests performed on Wacom pen tablets are available at the end of this discussion.
FACTORS FOR EVALUATING PEN TABLET ACCURACY
DEFINITION OF ERRORSSpatial Errors: Quantization error due to the finite resolution of the digitizer. This error occurs as a result of electric noise and mechanical imperfections. The RMS of this curve is used to estimate the spatial accuracy. As a rule of thumb, if the coordinate RMS error exceeds 3 resolution units, improving resolution will not improve the coordinate RMS error.
Temporal Errors: Temporal errors consist of missing or extra samples and frequency peaks in the frequency spectrum. As a rule of thumb, there should be no missing or extra samples and no frequency peaks in the frequency spectrum. (Frequency peaks can only be visually derived from the chart of the acceleration spectrum).
PRIOR TO TESTINGThe test is intentionally simple such that it can be conducted by anyone. Perform the test at least two times and use the best results.
Ensure that you have the most recent pen tablet driver installed. In MovAlyzeR®, go to the Device Setup Wizard to acquire the tablet settings. Create a new experiment, which will inherit the settings acquired from the Device Setup Wizard. Add a group, subject, and a default condition with the default number of trial replications: 2.
1. Place a non-conducting ruler on the pen tablet surface at a 45-degree angle.
2. Run the experiment that was setup above.
3. When the trial begins, draw a straight line approximately 10 cm in length, with the pen held vertically. Draw as fluently as possible, to ensure a consistent movement throughout.
4. Repeat for the second recording.
5. Right-click the first recorded trial and select "Test Linearity".
6. You can observe the straightness and smoothness results in the "Device Units vs. Sample Number" chart. The subsequent chart contains the Missing Sample Estimator.
7. Closing the Raw Data Chart, you will find the test results in the results window in the bottom section of MovAlyzeR®.
8. In the results window, you will find the spatial and temporal errors.
9. Repeat this process for the second recording. Using the best results, you can compare the calculated accuracy with that specified by the tablet manufacturer.
WACOM PEN TABLET ACCURACY TESTING RESULTSThe following pen tablets have been tested by NeuroScript. The full details can be found by clicking the tablet name in the first column.