4 ms·As far as I know, the Feynman Lectures have always used SI units.by mhartl 13y agoAs far as I know, the Feynman Lectures have always used SI units.drivers99 13y agoI just checked Chapter 4, and it has inches and ounces. I could be wrong, since I haven't read it, but I don't see why it would affect understanding of the ideas.mhartl 13y agoThe Lectures may occasionally mix in Imperial units, but the vast majority of the calculations use SI.