[Eeglablist] Why are power values different when a single channel is plotted vs multiple channels?

[Gan, Hock]

Hi,
This question has probably been asked before but my navigation aroung previous emails posted is poor.

I plotted a specific channel (say 12) on EEGLAB using <Plot> <Channel properties> in one instance and <Plot> <Channel spectra and maps> in another instance so that channel 12 was included in a group of 14 channels. When I looked at the plot, the specific values at a particular frequency (say 2Hz) was different for the two instances. I used spectopo to emulate the pop_spectopo and pop_prop and got 513 values of which I examined specific ones to have a clear look at the values. 

Before I include more details, "Is this an expected result?" "Is there some normalisation done for 14 channel display?" 

When I tried to emulate the pop_.... functions with spectopo I get consistent results whether 1 channel or 14 were attempted which was consistent with the single channel display (pop_prop) so my conclusion was that pop_spectopo does something different with my dataset. 

Thanks,
Hock