I have an existing frame that I'm putting into BikeCad Pro. I have all key measurements, but the head tube height appears to be a dependent measurement. When I adjust the measurement from the center of the down tube intersection with the head tube to the bottom of the head tube, the head tube height doesn't change, rather the down tube slope changes. Therefore, I can't input the correct and measured height of the head tube. Your guidance is much appreciated. If you like, I can email you the file that I'm currently working with.
Your question touches on two subjects that are covered in video tutorials. Check out: bikecad.ca/toptube_frontcenter and bikecad.ca/tube_extension. Let me know if you still have questions. I'd be happy to take a look at your file if you e-mail it to me.
Emailed file over a bit ago. Please check it out when you have moment.