I'm trying to calculate the characteristic impedance of a surface microstrip 
using equation 4-4 found in the IPC-2141A errata. 

with the inputs of t=.035mm, h=.794mm, w=1.5 and Er=4.2 I calculate 
Z0=88.8 Ohms. However, when I plug these numbers into the numerous online 
calculators I get varying values all close to 50 Ohms.

Has anyone else used this formula and verified it is correct? 

Also, by the way the equation is written it appears that the pi^2 term at the 
end of the equation outside of the square root function. Is this correct or 
should it be inside the square root function?

thanks

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