For the power nerd cross-trainers. I couldn't find the equations explicitly written out anywhere, so I
input different paces and slopes into WKO and plotted the results. I
got:

NGP = pace + C*slope*pace

where pace is the speed measured by your pod/GPS and slope is "rise
over run". C is some constant, I don't know what physical principle
it's based on, but C~17.2 if pace is in m/s.

rTSS is just like TSS. The WKO website alludes to this but doesn't
write out the equations:

IF = NGP / threshold pace
rTSS = IF^2 * duration *100

(also posted on the Google Wattage group)