constant of proportionality

sorry i cant post in the electronic theory forum so im here..

this question is regarding amplitude modulation

for AM, the modulation index is given by
m=Em / Ec

However, some sources include a constant of proportionality where
m= k (Em/Ec)

what is this constant of proportionality ? and is it necessary to be added into the formula?

thanks..

It could be used to give you modulation depth in percent if k = 100.

oh its for that!
i thought it was some complex thingy ive never been acquainted with...
thanks a million=)