# Need help understanding off axis electromagnet field strength equation

I have this equation for the magnetic field strength of an electromagnet but it’s in the form of multiple polynomials. Here is the page where they all are:

http://www.netdenizen.com/emagnet/offaxis/solenoidoffaxis.htm

since it gives values for e_8 and p_8 I tried using the main equation up to the 8th power but when I plotted the parallel distance against the field strength I found that it increases drastically to the point where at 5cm away the field strength is 1 Tesla (the strength I already know is B_0 which is the strength at the centre of the electromagnet and that’s only 0.03 Tesla)

So obviously the way I tried using it is wrong because the field strength should decrease the further away your measuring.

Can anyone help me figure out how to use this equation?