It was the same page I already had!
On synthetics - I ASSUME that the LAST value on the stack is what is returned. I could not find a basic how-to or syntax for the synthetic variables - OR the language they use. Makes debug very hard.
Here is my synthetic variable calc - which is NOT validating:
length = 15000
height = 10000
radius = height / 2
rsquare = radius ** 2
specialheight = where( liquidheight > radius , height - liquidheight , radius - liquidheight )
thetaradians = 2 * arcos( specialheight / radius )
specialvolume = rsquare * ( thetaradians - sin( thetaradians )) * length / 2
volumemm3 = where( liquidheight > radius , ( rsquare * pi * length) - specialvolume , specialvolume )
volumegallons = volumemm3 * 0.00000026417
specialheight ## put here as a spoof so I could save the formula in the synth variable