Finding Additional Resources

As you can see, complex families like this require a lot of formulas to properly constrain. Revit's help documentation is quite good at explaining the specific syntax to use in the formula fields, but it doesn't help you with finding the right formula for the geometry you're wanting to control. Here are some tips and websites to turn to for help with formulas:

Excel Not surprisingly, Excel has the formula game down pat. If your formula in Revit has a lot of parentheses or commas and you are getting errors that the end of the expression is “unexpected,” you probably misplaced a parenthesis or comma. Copy your formula into Excel and it will color-code your commas and parentheses so you can find where you're off. Revit and Excel have similar formula syntax, so if the formula works in one, it will work in the other. Don't have Excel? Many other spreadsheet applications have similar functionality.

Wikipedia If you're struggling with geometry, there is a wiki page ready to help you. Wikipedia's math pages are very thorough and give you almost everything you need to calculate that versine of the chord in your circle. You can search for Circle, Triangle, Ellipse, or Schrodinger's Cat online at Wikipedia.

MathWorld Still not finding that last pesky little formula? MathWorld is another free site that provides cryptic definitions and formulas that might just make the difference between approximating a solution and making it work perfectly (mathworld.wolfram.com).

Wolfram Alpha So, you found your formula but algebra isn't your strong suit? Problem solved (pun intended). Wolfram Alpha is a sister site to MathWorld with one big difference: It solves equations for you. Type in the formula you found on Wikipedia, and tell Wolfram Alpha to solve for whatever variable you need. The site will do the computation, and even show you all the steps—just like your high school teacher always wanted. It also does lots of other neat tricks, and even has an app for your phone (www.wolframalpha.com).