Reticular vector gauge

A reticular vector gauge was a device with an unspecified function. At least one of its components was made of glass.

The Fifth Doctor visited Androzani Minor to get sand to make glass he needed for his reticular vector gauge. (PROSE: So Vile a Sin) When he found some sand that had been fused into glass from a rocket and wondered why its crew had come there, Peri asked if someone had wanted sand to make glass so they could blow a new vacuum tube for their reticular vector gauge. The Doctor noted this as sarcasm, which he said was not her strong point. (TV: The Caves of Androzani)

In a parallel universe, the Doctor picked up the glass he needed for his reticular vector gauge at a market on Heaven and never visited Androzani Minor. (PROSE: So Vile a Sin)