I'm trying to get something straight. The multiplicative inverse or reciprocal is y=1/x, suggesting you just flip one to get the other. Can that numeral 1 sometimes be any number (in which case you're no longer flipping it) and still be a reciprocal? Using the relationship between heart rate (bpm) and cycle length (in milliseconds), for example, HR = 60,000/CL. In this case the equation would read y=c/x instead. How does that change anything?