Size| 107(a)(b)Fig. 4.5Measuring “maximum” tarsus using the OD calliper of a Vernier. This
measurement is typically taken to 0.1 mm in species of the size of this European
(Wood) Nuthatch. Note that (a) the foot forms a right angle to the tarsus, and that it
is essential that the tarsus is held parallel to the calliper (above); (b) this measurement
can be taken on a wing rule (below), and that the two methods should give identical
measurements. (Photo: Andrew G. Gosler)