Thanks for the speedy reply, Tim.
Unfortunately I couldn't get that to work. Anything entered after < is ignored and deleted when I save the question.
Googling to check I was using the Unicode correctly (yep, I'm a teacher, not a programmer), I found an alternative solution.
I used the ² from the copy and paste section on this page and it worked!
https://www.sheetaki.com/subscript-and-superscript-numbers-in-google-sheets/
Unfortunately I couldn't get that to work. Anything entered after < is ignored and deleted when I save the question.
Googling to check I was using the Unicode correctly (yep, I'm a teacher, not a programmer), I found an alternative solution.
I used the ² from the copy and paste section on this page and it worked!
https://www.sheetaki.com/subscript-and-superscript-numbers-in-google-sheets/