Tool
Battery size check at true size
Calibrate once with a bank card, pick a code, and lay the old cell on the outline. For paper, print the true-size sheet.
Pick a code to draw it at 1:1.
Calibrate this screen
Screens scale pages differently, so true size is only true after calibration. Hold a bank card or ID card (85.60 mm wide, ISO/IEC 7810 ID-1) against the bar and slide until the bar is exactly as wide as the card.
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Screen sizes are approximate even after calibration. A ruler or calipers on the cell itself beat any screen.