@Derrel did you have a chance to determine the accuracy of the calculated aperture, ISO, distance or fall off?
I don't own an Einstein monolights,but I went to Buff's site and their Expected Output chart confirms by actual meter reading the 102 GN with their softboxes. The Speedotron D402 GN figures are reliable, dating back to the era before most people owned a flash meter, and actually relied on the GN method.
The falloff computing that the app offers is something I have never seen offered before: the power of Android computing.
Buff's web page, Expected Output confirms by actual meter readings the GN of the app. What I really wanted to know was the relative true power of the Einstein 640. When comparing two different flash units, the beam spread of the light is a critical factor. Buff data days the AB B1600 at Full power and their Einstein E640 at full power are
640 - 660 watt seconds,
With a Guide Number of 155 using their standard 7-inch 80 degree reflector. What the older Speedotron power pack lists as a GN of 150 is an output level of 200 Watt-seconds using the D402 power pack and that system's 65 degree beam spread reflector.
When comparing flash units, product model numbers are not very useful. For example the Alien Bee B1600 model and the Einstein 640 are both listed as an actual 640 - 660 watt seconds of output. With their standard 7 inch 80 degree reflector the Guide Number is 155, but with the Speedo D402 ( 400 W-sec, 4- outlet) pack set at 1/2 power with a 65-degree reflector the Guide Number is 150. As one can see we have flash units labeled 1600, 640, and basically 200, all creating the same Guide Number. With different beam spread angles.
The ability to choose from a list of flash units, or to enter in revised or modified guide numbers is very useful. For example switching from the 7 to the 8.5 inch, 45 degree high output reflector in the Alien Bee Line, boosts the guide number by 1 full EV.
