How to calculate the font width, ZPL

I wanted to ask how the font width is calculated?

For example, in the ZebraDesigner program, I have a 12 pt field, the Zebra0 font

in ZPL language: ^A0I,34,33

For 203 DPI: 12 * 203 / 72 = 34

But how is the value "33" calculated?

The average character width for Zebra0 12 pt is 4 (GetTextMetrics), but I do not know how to calculate it.