Distance Points Calculator

I was looking for a simple app to calculator the distance between two X Y Z points on a graph. This app looked perfect, EXCEPT for one major flaw: you cannot enter a negative value for X Y or Z! That makes this app completely useless. I reached out to the developer, with no response. If this app allowed the user to enter negative values, it would rate five stars. As it is now, I would give it zero stars if I could, and ask for a refund. Do not waste your money on this product.