What did you do to give floatmultiplywith a value?

You are using a QSpinBox (QDoubleSpinBox) which will give an int (or double) when value() is called regardless of the prefix or suffix settings. By grabbing the text() value you get a string including the prefix/suffix when you really want the value. Calling cleanText() would be closer but you still have to manually convert to int/double. In short, if you want a number don't ask for the value as a string.