Inside a cheap set of eBay digital calipers

For such a lightweight plastic measuring device, the resolution of 0.1mm or 0.01″ and repeatability is quite astonishing. Whilst not being suited to a professional machinist, these units are ideal for ordinary measurements, including designing 3D printed components.

It should be noted that the quiescent current of these devices is around 18uA, even when off (the display goes off until movement is detected). Some users are reporting a very short battery life, but a typical 100mAh (0.1Ah) button cell should be able to supply 0.00002A for a very long time. (Theoretically 100’s of days.)

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