7.5 Numbers, letters and reference signs
7.5.3 Height of the numbers and letters in the drawings
A minimum size of 0.32 cm is required for all numbers and letters used on the drawings so that their reduction in size to two-thirds remains easily legible.
The Latin alphabet should normally be used for letters. The Greek alphabet is to be accepted however where it is customarily used, e.g. to indicate angles, wavelengths, etc.