I'm slightly confused about natural units. Take mass as an example: I can measure something in kg's, but then decide to convert to MeV/c^2, for instance. To do that I would multiply the quantity in kg by 3*10^8 squared and divide by 10^6*1.6*1-^(-19) i.e. the SI values of the constants. If I then want to express the mass in natural units, which would be MeV instead of MeV/c^2, would I multiply by 3*10^8 squared again?