Why do cartridge manufacturers give a range for VTF?

t_e_p, how did you delete your post?

Recently I posted a question, then the next day found my answer.  So I attempted to delete it but could not find a way.  No one had responded to it yet.  All I could do was erase the content and mark it "removed".

Threads themselves can be deleted and removed by the OP for sure, unless Audiogon changed that in last few days.
Done it myself on more than one occasion.

In most cartridges the coils sit between two magnetic poles. The magnetic energy between  the poles is even so position within the gap is insignificant. The only exception I can think of is one Van Den Hul model that only has one pole. So the recommended VTF is a trade off between tracking ability and stylus/record wear. Again the test record is the ultimate way to determine the right VTF using the manufacturer's range as a starting point. I will use the lightest VTF that makes it through the tracking band. Sometimes this lies outside the recommended range. So be it. There are too many variables for the manufacturer to be able to predict.  What ever produces the best results is the right VTF. Without a test record you are just guessing. 

@pryso 

I deleted my post within 2 minutes of posting it.  I think my options were "edit" or "delete" and I chose delete.