I have inserted a reference plane as shown in the picture below. I'm trying to specify the distance to a few decimal places. At first it would only accept integer numbers. Can anyone tell me why? It somehow fixed itself but I want to understand what happened.

But what I really want is to enter a formula or variable because the distance is related to the length of the base of the pyramid. Is there a way to do that? I think I could go back to my starting 3D sketch (dashed lines in the picture) and set a reference line if this doesn't work.

Thanks everyone.

Maybe you have your dimension precision set to "none", meaning no decimal places. Tools >Options>Doc Properties>Dimensions to sort that out. You might also have your grid/snaps turned on. Snaps are under Tools>Options>Sys Options>Sketch>Relations/snaps.

To get the equation, you can just use the Modify box for the plane, and make sure you have a good name for the sketch dimension from the triangle. I've named mine "TriSide". You can name a dimension by just selecting it, and changing the name in the PropertyManager (to the left). To write the equation, just use the equal sign in the plane offset distance Modify box (double click the plane, double click the offset dimension that pops up).