After reading Peter King's latest article in MEW, I tested two digital calipers, a cheap(ish) digital micrometer and a 50p Starret micrometer from a bootsale.

On a 25mm test bar the two micrometers and the cheapest (Aldi) caliper all agreed to 0.01mm (I had to compare the Starret with the metric reading on the digital mike). The other caliper was 3-4 thou low.

On some nominal 0.625" stock, they all read either 0.6235" or 0.6240", except the 'dodgy' caliper which had lost about two thou.

After vigorous cleaning (spit & thumb) of the scale on the dodgy caliper, it miraculously regained its accuracy!

So three thoughts:

• Cleanliness, once again, is next to godliness in model engineering.
• Old micrometers might not have had as tough a life as their age suggests.
• Cheap stuff isn't necessarily nasty.

For the record, the cheap 0-25mm/1" digital micrometer also has a 'normal' scale, which agrees with the readout.

Neil