Norton Creep parameters

Hi

I 'm simulating the creep of polycarbonate part under a constant load and constant temperature during the time.
I used the Norton model, but I've got some doubts about three parameters: stress exponent, Creep rate coefficient and Reference creep stress. I explain shortly about the procedure that I got these parameters I really appreciate if anybody could say are these correct or not.

n:
I found the stress exponent by using the natural logarithm of strain versus stress, which gradient of this graph is equal to n.

Q/R:
Then I used the natural log of creep rate against the reciprocal of temperature to find The activation energy Q. The gradient of this graph is equal to -Q/R.

Then I used the relation Δέ/Δt=A(σ^n)exp(-Q/RT) for the constant temperature and stress to calculate the A (creep rate coefficient). But the unit of A is 1/(s.pa^n).

How can I extract 'creep rate coefficient' with unit 1/s and 'Reference creep stress' from calculated A?

Am I in the right track?

I really appreciate every hints.

Best regards,
Samira