the rotor or the big calculator

Fill all Radius in cm, with range [minimum .. maximum ] and push "Calculate".
To print it go to your browsers drop down "File" menu and select the "Print.." menu.

OuterRadius in cm [1 .. 400]
InnerRadius in cm [0 .. 400]
InsideRadius in cm [1 .. 400]
NumberOfCells [4 .. 204]

Arch means how much degrees of a complete cirkel (360 degrees) is covered.
Eff. surface is the surface of the OuterRadius minus surface of InnerRadius.
One bridle is the length of 1 single bridle line.
Stop sewing is the measure were you should stop sewing when you sew 2 cells together.
Arch length is the circumference of the arch in cm.
Min.Req.Fabric is the minimum estimated square meters of fabric that you will need.
Total bridle is total lentgth of all bridle lines + knots.
Flap size is the measure of the flap height.

Example with: 50 cm outer, 30 cm inner, 20 cm inside, 24 cells.
Draw a horizontal line on the top of a sheet of paper (-),
in the middle draw a vertical line (|), together it looks like a T.
The 0.0 cm is the horizontal line (-).
At this horizontal line (-) set marks left and right of the vertical line (|) at 3.9 cm from the vertical line,
At 2.5 cm from the 0.0 cm line draw a horizontal line (-) with marks on it at 4.25 cm from the vertical line,
etc, etc.