Improving Extraction Accuracy

Understanding Error Margins

Total extraction error ($E_t$) is a combination of:

1. Resolution Error: The mathematical limit of pixel mapping.
2. Calibration Error: Inaccuracy in your initial axis clicks.
3. Tracing Error: Not clicking the exact center of the data line.

1. Maximizing Resolution

Never extract from a thumbnail. Always zoom into the PDF or presentation to maximum size before taking a screenshot. A 400x300 pixel chart has vastly higher resolution error than an 1600x1200 pixel chart. Check your image with the Resolution Checker.

2. Perfecting Calibration

The most common mistake is picking calibration points too close together. If your X-axis goes from 0 to 100, do not calibrate using 0 and 10. Calibrate using 0 and 100. The wider the spread, the lower the angular error multiplier.

3. Center-Line Consistency

If a data line is 4 pixels thick, always aim for the exact center pixel. Consistently clicking the "top" of the line will shift your entire dataset upward by 2 pixels of logical value.