On Mon, 23 Nov 2009 17:40:36 -0800, Michael Koblic wrote:

I have three sets of cheap digital calipers bought in Canadian Tire. The
have all been working fine and agree with a micrometer to within 0.001".
Two weeks ago I tried to use the one I keep in the workshop to measure
something of the order of 4" when the calipers refused to measure
anything past 1.5". I brought them into the house where they started
working fine as soon as they warmed up.

Your description makes it sound like a cold-temperature-related
problem, which surprises me because my Harbor-Freight-type
calipers work ok at 3 - 4 C (except for it being clumsy to
operate the little buttons when wearing insulated gloves).

The second set did exactly the same thing today.

Try the third one, or better, all three of them in the
same time frame and environmental conditions. Also, try
zeroing the caliper when it is open about an inch or two
and see how far it works each way, and test whether the
metric scale has the same problem.

The temperature in the workshop is 9.5 deg C.

Replacing the battery made no difference. What is the likely cause?

Maybe they are too cheap and you need to upgrade to
superior HF quality calipers. BTW, re low batteries,
aside from the LCD blinking (to signal low battery) my
calipers seem to work ok for several months with low
batteries, even in the cold. (I keep ok batteries in
several calipers, but for the less-frequently used ones
change the batteries less often.)

--
jiw