Round off numbers
I recently added new code to my 100,000 line accounting program. In this new part I subtract one variable from another and display the result in an edit field. The result of subtracting variable values 252.26 from 1000.25 is displayed as 747.889999999 rather than the correct answer of 747.89. As a test, I hard coded (no variables, just numbers) the same equation for display in a test window and had the same result. FB does this same thing for some but not all number combinations. For example the equation 1000.25-252 displayed a correct result. I am not sure if this problem has existing for a long time and I just never noticed it because of program rounding procedures.
What you are seeing is not a bug. Instead, it is an artifact of the way binary computers represent floating point values. Just as there are rational numbers (numbers that can be exactly represented as the ratio of 2 integers) that have infinitely repeating decimal expansions (like 1/3 = 0.333333...) there are binary numbers that possess the same characteristic. This is a normal occurrence in all binary floating point calculations.
Some systems represent floating point values internally in BCD format rather than true binary format, precisely as a means of eliminating that rounding error in decimal representations. When stored as BCD values of sufficiently high precision, 1000.25 should be stored as _exactly_ 1000.25, and 252.26 as _exactly_ 252.26.