Re: Weight
I'm going to be really pedantic here, so I expect to be shot down by VoT, but weighing things at different places on the surface of the earth with the same equipment gives different results as a result of gravity not being constant on across the entire Earth's surface.
The force applied to an object (and thus it's weight) is dependent on the distance between the centre of gravity of the two objects. So altitude matters, and as the Earth is an oblate spheroid so does the latitude.
In addition, the density of the earth is not uniform, so the centre of gravity of the Earth is not exactly at the centre of the Earth, resulting in some descrepancies at various points on the Earth's surface.
The difference will not be very large (varying by about 0.5%), but it's a counter argument to the comment about 99.99999999% of the people who have ever lived being under 1g.