I have been using this method http://www.cartertools.com/involute.html to draw gears with Draftsight but I am wondering if there is a way semi automate step no 5. At the moment I am multiplying  the value of tangent line by the number of the radial line by hand so it time consuming.  Is there a way to get draftsight to calculate the tangent line length value automatically from the first value input.

Hope the above makes sense and you can help

Bill