Nine points of measurement
Ball girth is the one that fails a fitting. The other eight are the ones that make a shoe you keep wearing after it fits.
Nominal size is a length. It tells you almost nothing, which is why two pairs marked 43 can differ by 8 mm of stick length and 12 mm of ball girth without either being mislabelled.
Ball girth is the circumference around the widest part of the joint. It is the measurement that decides whether a shoe hurts. Every other number decides whether you notice the shoe at hour six.
Two pairs marked 43 can differ by 8 mm and both be correct.
Toe spring is how far the forepart lifts off the ground at rest. Ours runs 8 to 12 mm depending on the last. Too little and the sole fights every step; too much and the shoe rocks when you stand still.
Stick length is measured along the last, not the foot, and it is the number to use when moving between our lasts. The retired LF-02 runs 6 mm long against the LF-07 at the same marked size. That is a half size, and it is why the Archive pairs carry a warning.