// in "Animate a Pendulum"

  SET( px,  640 )//65 )
  SET( py,  30 ) //7 )

// long of the line:

    LET( bx := ADD( px, MUL( MUL( l, 180 ), SIN(theta) ) ) )
    LET( by := SUB( py, MUL( MUL( l, 180 ), COS(theta) ) ) )

// and circle ratio:
    {bx, by, 10} GOSUB( CIRCLE )