For those using conventional gear hobbers:

- After determining the ideal ratio needed to fabricate a helical gear,
how do you determine the best combination of (A/B)*(C/D) in your
gearbox that closely approximates the ratio?

- how often do you need to change your gear setup?

- how long does it usually take for you to find the right values for A,
B, C, and D? (half an hour? an hour?)