Yeah, that's the question Rob's asking
That figure 450240 = 7000 x 2 x 32.16
32.16 is the constant for the acceleration due to gravity.
But.... 32.174 is the International standard value for the constant and in the UK the figure for gravity is around the 32.19 - 32.20 mark.
I think whatever way you look at it 450240 is the wrong figure for us to use.
If you use the figure 450436 ( international standard for gravity of 32.174 ) then your 11.940 figure becomes 11.935
Does it matter? Nah not really