Stock F1 / F2

[rc_daz]

On the original entry form there was only one box for Stock, there was no 'F' categories. On the results table they have been split into F1 and F2. Where was the information taken from to decide whether someone was an F1 or F2 driver?
What is the actual difference between the two?

[spannersatcx]

From the entry form:

This Class will be split into two Formulas:-
F1 Drivers with a Grading of 83% + F2 those with a grading of
below 82%.

I think the gradings are based on last years results. Any new drivers automatically go in F2.