Reduce every value to a single digit: 200 → 2, 400 → 4. Ἰησοῦς is 888 → 8+8+8 = 24 → 6; θεός is 284 → 2+8+4 = 14 → 5. The pythmen ('base') of a name is that digit.
Meaning
The Greek counterpart of mispar katan, and the bridge by which isopsephy became the arithmetic of the medieval West: a name's pythmen puts it under one of the nine numbers whose qualities the arithmologists catalogued. It is the operation behind every 'number of a name' in the handbooks, and the reason a single digit could be made to carry a whole biography.