Well, by my math, knowing the height of the steps is 54mm, the line through the tread nosing each step on the 27° face should be 22.22°. Your mileage may vary, but it shouldn't.
Starting on the square side of the stepwell, in elevation.....
TAN(20°) = nose of top step to nose of bottom step / 54mm
nose of top step to nose of bottom step (square side) = 19.654mm
Now in plan, figure out the distance along the angled side from nose of top step to nose of bottom step......
COS(27°) = 19.654mm / nose of top step to nose of bottom step
nose of top step to nose of bottom step (angled side) = 22.058mm
Now back to elevation to determine the angle of the line from nose to nose on angled side of the stepwell.....
TAN(angle from nose to nose) = 22.058mm/54mm
angle on angled side of stepwell = 22.22°
It's a little different then what I described above, but it works out the same. Sometimes one sees things more clearly than they did initially.
Have fun!
Jim
