1.15-1.13=0.1999998 ? Please help

Floating point math is inherently inaccurate. If you want accuracy, you MUST use decimal types. Yes, it's a hassle to convert before doing the math, but it's necessary if you want guaranteed precision.

BTW, a float (or double) will maintain it's value until you perform a math operation on it. At that point, it's value is NOT guaranteed to be completely accurate, and comparisons are not guaranteed to have the results you expect.

Using decimal is the one true path.

Try it this way:

MyResult = Convert.ToSingle(Convert.ToDecimal(MySingle1) - Convert.ToDecimal(MySingle2)) 

And see if the value isn't precisely what you expect.

To avoid the casting, simply start using decimal for all of your Single or Double variables.

ALTERNATIVE - use the Math.Round method to round to a certain precision, but that's fake math. I prefer the precision of the decimal type (even though it takes a little longer to do math ops on them).

I suspect that there is little or no difference - it may well be the way you are outputting the numbers, rather than the values themselves.

However, if they are in different projects, are all the options the same?
Is one 32 bit, and the other 64?

You can also write this

Dim MySingle1 As Decimal = 1.15
Dim MySingle2 As Decimal = 1.13
Dim MyResult As Decimal = MySingle1 - MySingle2