Cecil Moore wrote in newsHiPh.3364$YL5.1126
@newssvr29.news.prodigy.net:

....
simply drop the units of area. The resultant "irradiance"
equation for transmission line power is:

Ptotal = P1 + P2 + 2*SQRT(P1*P2)cos(A)

2*SQRT(P1*P2)cos(A) is the interference term in watts
where A is the angle between the two interfering fields.

Is this what you mean by 'algebraic sum' as in your words 'resultant
disturbance at any point in a medium is the algebraic sum of the separate
constituent waves'?

Owen