I've been trying my index expression after changing field type from numeric to currency: STR(price,16,2).
As -922337203685477.5808 is the low limit for CURRENCY type numbers, I tried it in a command window:

x = -$922337203685477.5807
wait window STR(x, 21, 4)

I expected '-922337203685477.5807' string but got '922337203685477.6000'.
After some investigation I found that STR() prints only 16 most meaning digits rounding the rest:


str(-922337203685477.5807,21,4)=='-922337203685477.6000'

str(-022337203685477.5807,21,4)== '-22337203685477.5800'

str(-002337203685477.5807,21,4)== '-2337203685477.5810'

str(-000337203685477.5807,21,4)== '-337203685477.5807'


Or maybe it's an effect of some misterious SET?