On 2011-11-21, Martin Riddle wrote:

wrote in message
...
On Nov 20, 8:45 pm, Jeff Liebermann wrote:
On Sun, 20 Nov 2011 16:47:25 -0800 (PST), "Ron D." wrote:

I have a cheap Caliper too and it recently went flakey.

[ ... ]

same size. Where you can have problems is that the SR44/SR1154
silver
oxide cells come in the same package. They have about 50% more
capacity and a much flatter discharge curve. Some of the cheapo
calipers crap out below about 1.4V. The alkaline battery has plenty
of capacity left at 1.4V, but the caliper doesn't want to run. If
your caliper cames with a silver-oxide cell, it should probably use
silver oxide batteries. If it came with alkaline and has a short
battery life, it might be worthwhile trying silver-oxide. If you're
ambitious, it might be useful to run the caliper off a bench power
supply and check how low a voltage will work.

I just measured a Harbor Freight (Chinese) 8-incher.

Drain: 13.5uA (off), 14.5uA (on)
Battery low threshold (blinking display): 1.37V
Lowest operating voltage: 1.01V

So, it's clearly made for silver-oxide cells. The battery low
threshold is set appropriately for a silver oxide cell (e.g. SR-44).

It's a lousy threshold for using alkalines--they're barely broken in
at that voltage.

14.5uA means a year from a silver oxide cell--that's not horrible.

[ ... ]

Why bother including an on off switch?

It is an off switch to turn the *display* (only) back on. They
sometimes make it also turn the display back off to make people feel
better. :-)

The auto-turn-off time of the display is usually good enough.

Enjoy,
DoN.

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