Wasn't it Mike Williams who wrote:

>#declare F1 = 17;       //frequency of right end only a few magic values work
>#declare F2 = 43;       //frequency of left end only a few magic values work

The magic values for F1 are about (4n+1.3)*pi and for F2 are about
(4n+1.7)*pi where n is an integer.

To get a scroll that curls in the same direction at each end, change
       #declare Y=sin(T*F1)*((R1*(0.5-T))+(R2*T));
to
       #declare Y=-sin(T*F1)*((R1*(0.5-T))+(R2*T));
and then the magic values become (4n+1)*pi and (4n+2)*pi.

-- 
Mike Williams
Gentleman of Leisure

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