Where did you get the notion that g can be as low as 8.3? AFAIAA on Earth's surface it ranges from 9.781 ms^-2 at the equator to 9.832 ms^-2 at the poles. There are further variations due to topography, but I don't think these ever exceed a thousand mGal (1 mGal ~ 10^-5 ms^-2)

To find your local gravity, use the International Gravity Formula:
g = 978.0495 (1 + 0.0052892 sin^2(p) - 0.0000073 sin^2(2p)) cms^-2, where p is your latitude. (No, I don't know why the IGF is not nowadays given in SI units.)

Or, in other words, if you use 9.8 (or even 10) you're not going to be off sufficiently to make an important difference.

HTH

Later addition: I've just recalled the unit of local variation in gravity: it is the Eotvos. 1 E = 10^-9 s^-2. The vertical component is 3000 E per metre, i.e. 3*10^-6 ms^-2 per metre elevation.

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Stephen