Even 9.81 m/s2 is not accurate. I use 9.8165, why because when I am doing calibrations using mass I have to and if I need more accuracy I use an even longer version of G.

To add to the complication the G figure above is standard G there is also local G. The variation of G increases as you get towards the equator, you'd weigh slightly more at the equator than you would at the poles. It also varies due to whatever is under the ground near you locally, large amounts of iron bearing rocks and underground oil have a small effect on G.

Rounding up is just not on, bet when these kids grow up they would not round up the level of their pint if it has been delivered slightly short in measure.

Now I will go away and find a clean anorack and go trainspotting.