THIS APP IS INTENDED FOR FLIGHT SIMULATOR USE ONLY. DO NOT USE FOR REAL-WORLD FLYING.
DH8D TOLD is intended for use with Majestic Softwares Dash-8 Q400 add-on for Microsofts Flight Simulator X and Lockheed Martins Prepar3D, but it should also work with most other Dash-8 Q400 add-ons.
It computes the masses of the aircraft as well as the relevant takeoff and landing speeds, which you would normally derive from the speed tables provided with the aircraft or the so-called TOLD Cards used on the flight deck.
You can purchase the Q400 add-on from Majestic Software here: http://majesticsoftware.com/mjc8q400/products.html