In the opening scene, an arsonist piles combustible materials on Mr. Joseph's desk. Said combustibles are absent in the next shot of the desk.
A potentiometer is no more than a fancy name for a variable resistor, i.e. a volume control on a radio or a light dimmer switch. As usual, the PM writers have no clue what they are talking about.
Right after they have been scuba diving, Paul and Dorian still have dry hair.