Scale Adjust Jumps

Hello, I just installed this program today and I am loving it! But I have one problem, when I try to adjust the scale of a layer with the mouse it's not very accurate. Then when I type in 87 for example it jumps to 870%! And when I try to type .87 it works, but then I want to type 87.5% so I type .875 and it jumps to 875%! How do I get the decimals to work?

Thanks in advance!