This is also confusing as it states it should be a 38bit int but says it holds +/-13,743,895.3471meters.

(2^38) / 13743895.3471 = 2000. So the divisor is 2000

This thread started going off-track very early.

2

^{38} / 13,743,895.3471 is 20 000, not 2000.

A simpler way of looking at the problem is to examine the value 2

^{37} (don't forget the sign bit) = 137 438 953 472.

Look familiar? Now divide it by 10 000, giving the 1/10 mm resolution already mentioned.

I can't believe that converting a 64 bit IEE754 number to this representation is all that difficult using "long long" arithmetic.

It won't be fast, but things that use numbers with this sort of range rarely (in my experience) require speedy calculations.

However, if there is a similarly-priced platform that will handle 64 bit IEE754 natively, that's the solution I'd go for.