T=24h

Well, either he grew back 0.5cm over the course of the day...or my last photo was in fact angled. I'm thinking the latter. So...looks like my t=12h photo is not valid (there's always the one data point that doesn't fit). If I ignore that one, then he lost about 0.5cm over 24hours. I will endeavour to keep my phtotos as dead-on as possible. He's got such a big head, that the slightest angle skews the measurement immensely!