Local G in China varies by as much as 2% north to south.

According to my table(*) of local gs (not G, that's the universal gravitational constant), at the equator it's about 9.78 metres per square second, at the N pole it's about 9.83. That makes the range about 0.5%

They also give a very useful equation for deriving G at any latitude:

for latitude L (degrees I think, they don't say) and height h metres

g = 9.80616 - 0.025928 co2L + .000069 cos(sq)2L - 0.000003h

I bet you're glad you know that- all of you, write it down and keep it in your purse, you never know when you'll need it!

If I'm doing ball-park calculations, I use 10, the result is only about 2% out, and if you're talking about free fall remember you're not in a vacuum.

(8)R>M>Tennent, Science Data Book, Oliver & Boyd 1978.