Go Off on a __, Suddenly Change the Subject

This page is the CodyCross answer for the clue below from Past and Present Tech, Group 1459, Puzzle 1 (Graphical User Interface).

Question is: Go Off on a __, Suddenly Change the Subject

and the answer is: TANGENT

Word Meaning:

TANGENT — (differential geometry) A straight line touching a curve at a single point without crossing it there.

Definitions from Wiktionary.

Go off on a __, suddenly change the subject — CodyCross Answer | CodyCross Solutions