Originally Posted by

**ebaines** The accuracy of the first coedfficient is very important. You have 0,0001, but a more accurate number is 0.0010942. This is an increase of almost 10%, and when you multiply it by a large number like 120^3 it makes a big difference. Here's the math:

Your version:

0.0001(120^3) -0.0409(120^2)+4.6716(120)+280.32 = 172.8-588.96+560.59+280.32 = 424.73

My version, using 5 significant digits for the coefficients:

0.00010942(120^3)- 0.040896(120^2)+4.6717(120)+280.32 = 189.08 - 588.90 + 560.6 +280.32 = 441.10