Okay, here's what we need to get at, for starters. And maybe an illustration or three and a little exchange will go a long way towards helping my better comprehend units. I'm starting with a set of SI calculations for oil and gas constants calculations. Eventually we will need to accommodate US units as well. But not quite yet. We need to get at a calculation involving Pressure Gradient, which ends up being metric::bar/si::meter (bars over meters) in specific units, or I suppose si::pressure/si::length might also work. Then we need to get after Fluid Density, which ends up being si::kilogram/si:meter^3 (kilograms over cubic meters) in specific units, or I suppose si::mass/si::meter^3 (I don't know what this looks like in terms of boost::units, maybe one of the volumes?), or perhaps make use of mass_density? We take all that and divide Pressure Gradient by Fluid Density to arrive at what we hope will be the the conversion factor: 0.0000981. Which we could specify that as a constant, but I like proving it through the software first (plausibly once) when we ask for it. Similar type calculations would follow for US units involving gallons, cubic inches, inches, and inches per foot, along these lines. So I need some examples will spell it out for me. The learning curve using boost::units is just too steep for me right now without it. Any tips or pointers along these lines would be much appreciated. Thank you, Michael