Is there only ever 1 decimal in these numbers?
come before or after
yes there is only one decimal .... 1992.191 should come before 1992.20
Then if you are sorting in ascending order and 1992.191 should come before 1992.20, I don't see the issue. Make this a field of type number and sort in ascending order.
If the second value is seen as a second integer, such that 191 is greater than 20 instead of 0.20 is greater than 0.191, then you'd need to set up two calculation fields that extract (parse) the the numbers from before and after the decimal so that you can use those two fields in tandem in a specified sort order.