Subject: is it valid to use a microwave oven to estimate the speed of light?

I have seen a number of web sites which claim one can calculate the speed of 
light by putting a layer of chocolate chips on the floor of a microwave oven, 
running the oven until a few chips melt, and then measuring the distance 
between molten chips to determine the wavelength of the oven's microwaves.  
This value, along with the magnetron's frequency, can then be used to 
calculate the speed of light.

I'm suspicious about the validity of this experiment.  It seems like standing 
waves might exist along at least three axes -- top/bottom, front/back, and 
right/left.  If this is true, and I happen to measure between a F/B hotspot 
and a T/B hotspot, the distance is invalid for the purposes of calculating the 
speed of light.  For the demonstration to be correct, it seems mandatory for 
the waves to exist along only one axis.  Am I making things too complicated, 
or are all these websites wrong (including some at college physics 
departments)?  If I'm the one that's wrong, can you explain how the distance 
between any two molten chips is a valid measurement?

The dimensions of a typical MW oven and the wavelength "required" to caclulate 
the speed of light correctly are much less than an order of magnitude in 
difference, so it seems plausible that the demonstration is nothing more than 
a coincidence.

Thanks very much.  Sue.

Re: is it valid to use a microwave oven to estimate the speed of light?