In code (your m-file) you can get the min and max and make the step one over the range:
maxSliderValue = get(handles.slider1, 'Max');
minSliderValue = get(handles.slider1, 'Min');
theRange = maxSliderValue - minSliderValue;
steps = [1/theRange, 10/theRange];
set(handles.slider1, 'SliderStep', steps);
Put this in your GUI's OpeningFcn function or whenever you change the slider's max value (which you probably don't do in your program.)
If you do it in the Property Inspector and have 1 as the min and 80 as the max, you should set the small step to 1/79 = 0.012658227848101, and the large step as some multiple of that, like 2 or 3 times as large.
