#### Re: Risetime calculator (in tekwiki)

Roy Thistle

On Tue, Jan 21, 2020 at 09:08 AM, GerryR wrote:

why the different scales for the rise time
Hi GerryR:
Blue scale is 0 to 5
Black is double Blue so 0 to 10
And Red is double Black so 0 to 20
That's 2^0, 2^1, 2^2, for 1,2,4 multipliers.
If it is like others, of these type of simple analog computers, I've played with:
If you set A = 3, B =4, C=12, (3,4,12), on the Red scale, you should set F to sqrt(3^2+4^2+12^2) = sqrt(169) = 13 ... so you should set the F knob to 13 on the Red scale...push the button... and the bridge should be very close to balance... if the Rise Time Calculator has been properly calibrated.
I assume if you program in the numbers (2,3,5) on the Blue scale which gives sqrt(29), which is greater than 5, you would not be able to balance the bridge, and should reprogram them in on the Black scale.
I don't have one of the Tektronix Rise Time Calculators... so I am not sure that is indeed the way it works. (I'll try to check the math later.)
By the way, for those of us that love math... (3,4,12) = (13) is a solution to the quadratic Diophantine equation X^2 + Y^2 + Z^2 = W^2, such that all of X,Y,Z,W are integers. If you have a Tektronix Rise Time Calculator remembering that might help you.
Best regards and wishes.
Roy

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