First of all - Happy New Year
Day two of Ed's winter project to learn studio lighting. My question for the day is - with a wireless flash off camera what is the difference in the resulting image exposure between setting the camera EV at "x" and the flash at "y" as opposed to vice versa? Here's what I did & what I found. (Nikon D70, 18-70 lens at 70mm, f/4.5, 1/60 sec, SB-800 set to REMOTE, 45 degrees to left of camera, 2-3 feet from subject, umbrella, flash at 24mm).
Each ROW is done at a constant CAMERA EV setting. The top row is -2/3. Each succeeding row increases the camera's EV by 1/3 - so from top to bottom we have -2/3, -1/3, 0, +1/3, +2/3.
Each COLUMN is done at a constant FLASH EV setting. The left COLUMN is -2/3. Each succeeding COLUMN increases the flash's EV by 1/3 - so from left to right we have -2/3, -1/3, 0, +1/3, +2/3.
This places the darkest exposure at the top left (camera = -2/3 and flash = -2/3) and the brightest exposure at the bottom right (camera = +2/3 and flash = +2/3). The 0/0 (as metered) setting is dead center.
What can we conclude - every image on a diagonal going UP from left to right has the same "exposure" as measured by the SUM OF THE CAMERA & FLASH EV SETTINGS and they ALL LOOK ABOUT THE SAME regardless of the combination used. For example, look at the diagonal from the lower left CORNER to the upper right CORNER - this is a "net 0 EV" diagonal (the lower left is camera = +2/3 and flash = -2/3, the center is 0/0, and the upper right is camera -2/3 & flash +2/3). On the other diagonal - down from left to right - succeeding images increase in exposure by 2/3 of a stop.

CONCLUSION - FOR THIS SCENARIO AN EV OF "X" RESULTS IN THE SAME EXPOSURE FOR AN IMAGE REGARDLESS OF WHICH COMBINATION OF CAMERA EV "PLUS" FLASH EV WAS USED TO GET "X"

Tomorrow - try the same thing except vary the camera's contribution to the lighting "balance" by shooting in the manual mode and playing with aperture and shutter speed variations - and setting the wireless flash to Manual and varying its power settings directly at the flash rather than via the camera on board flash EV control. Since this seems to just be another way of setting the "EV" of the camera and flash, why should we expect to see anything different from what happened today? Tune in tomorrow and see.

Mama - don't let your kids grow up to be engineers ;o}