MetricMaster offers a nearly unlimited choice of units for conversion. However, being able to combine units would make MM even more useful. E.g. letting the users convert oz/yd2 into g/m2 in one step would be invaluable. MM was very unresponsive on my iBook/500/320 running OS X 10.2.4. It looks like MM 4.0.4 was just carbonized and still needs more work to make it the nice OS X app it can be. This is a good app, but there is room for improvement.