Theory:Doctor Who television discontinuity and plot holes/Full Circle


 * Romana says that the TARDIS weighs 5x106 kilos 'in your gravity' (i.e. 50,000 tonnes), which doesn't really explain firstly how the Marshmen can easily pick it up and also numerous references in other stories (DW: Marco Polo, Army of Ghosts, etc.) to the TARDIS being light enough to be lifted by a group of men.
 * It is possible that the gravity is different to Earth's or that the TARDIS's mass is variable.
 * The gravity is clearly similar to Earth's, as everyone moves around just as on Earth and has an Earth-type physique - and water waves are the same shape as on Earth too. It's possible that Romana is referring to the mass of the TARDIS's internal spaces. If the exterior of the TARDIS weighed 50,000 tonnes it would sink deeply into the soil or destroy floors at most of its landing-points - and could not possibly float as seen in Fury from the Deep.


 * How did Adric get to the Rebels without passing The Doctor or any Marshmen? And how did the Rebels get back without seeing them?

That's a pretty trivial difference. Most likely, he either didn't remember whether he pulled one of the many levers or flicked one of the many switches, or he is simply using the terms interchangeably. On an electronic controlk console such as that of the TARDIS, a lever is basically just a big switch.
 * When Adric flys the TARDIS by accident he says he must have pulled the wrong lever when he flicked a switch.