To avoid erroneous readings and unnecessary calculations, start your taper inspection from the smaller diameter, and progress towards the larger diameters.
For internal threads, measure the first interval closest to the back of box. For external threads, measure the first interval closest to the pin’s nose.
For example, if the reverse procedure is followed on a ¾” TPF 8 round thread, the dial indicator would read 0.038″ instead of 0.062″.