Guide Number Math

I need some help with guide number math. :oops:

in the following setup:

Nikon D100 Min ISO 200

Ikelite 200 GN 38

Ikelte DS-125 GN 32

I understand the following

Since ISO is 200 I have to mulitply the GN * 1.4

Ikelite 200 *GN 53

Ikelte DS-125 *GN 45

Where I am lost is what happens when the two strobes are on together

Is it something like

((53+45)/2)*1.4 =68

I think I read the formula in a book called "Using the Nikonos V", by Jim or Cathy Church. I don't own the book.

I think most people ignore the fact that there are two strobes, since apparantly, the arey not additive as we would think, and do the math as if there was only one strobe.

I am no expert.

I need some help with guide number math.  :oops:  

in the following setup:

Nikon D100            Min ISO 200

Ikelite 200             GN 38

Ikelte DS-125        GN 32

The manual of the Sea&Sea YS90 DX mentions that the resulting GN from using two strobes is GN = SQR(GN1*GN1+GN2*GN2)

in your case SQR(38*38+32*32) = 49.7. Since the ISO is 200 you have to multiply this result by SQR(2) = 1.41 to obtain the new GN = 70.