Body temperature fluctuations, with a minimum before waking and a maximum in the afternoon, indirectly measure circadian rhythm.

“your uh temperature levels in your body this fluctuates this is maybe one of the easiest observable differences in a human basically as a call it as an indirect measure of the Circadian rhythm where we basically see that you have a minimum point that happens typically in the morning just before you wake up and then you have a maximum Point typical in the afternoon”