A scale would be useful: Recommended dosage | ----|-x------------ vs ----|------------x- Also for mg vs mg/kg, that's a harder problem

A scale would be useful: Recommended dosage | ----|-x------------ vs ----|------------x- Also for mg vs mg/kg, that's a harder problem - off the top my head, get rid of the modes, and show both mg/kg and mg textboxes, with a radio button to select the one you want to edit. Edit it, and the non-selected text box is grayed-out and uneditable, and shows you the corresponding calculation (enter in mg/kg, and it shows you the mg amount of medicine; enter in mg, and it shows you the mg/kg ratio).