Philip Freidin wrote:
big snip
Using an SR44:

So, for a Mitutoyo that is on for 1 hour per day ...
Battery life is therefore 135000/50 = 2700 days = 7.39 years
The self discharge of the battery will probably make it
half this duration.

I.e., 3.7 years

Here it is for the chinese calipers...
Battery life is therefore 135000/420.5 = 321days = .87 years
....

So, if the Mitutoyo costs $36 (the lowest price for a new one that I
found on eBay - completed auctions), the HF Chinese one is $16, and an
SR44 is $.99 (my recent cost on eBay), we have:

$36 + .99/3.7 * years = $16 + .99/.87 * years, and then

years = 23

I.e., in 23 years the costs will be the same, ignoring the time value of
money and ignoring buying replacement calipers because your son used it
to take apart his bike, or you dropped it, or set your chuck on it, or
.... something 8-)