You can do this by getting the log base 10 of the number. [[expr log10($number)]]

You can get the regexp of the number, and then get the string length of the digits to the right and left of the decimal point.

In my case, I had a variable called precision, which determined how many places beyond the decimal point were displayed.

So, for precision = 2, .007 would be displayed as .01

To determine if this rounding was occuring:

	    set non_rounded_number $my_value
	    set rounding_p [expr (-1 * log10($non_rounded_number)) > $precision]
	    if {$rounding_p} {
		# we have rounding
	    }


[[
[Category Mathematics]
]]