For single tree calculations the dia is hard-coded to 5.09999990463257. This causes confusion with the dia that is sent for calculation doesn't match what is entered in the text box on the screen. I changed this so it now reads from the text box.
For single tree calculations diahtdcd is hard-coded to 1. I changed this to a combo box where 1 and 2 are the available values. 1 is the default.