Hi Neil,
"Not quite...from me it was the Alt (or Option Key) followed by the letter "I" . this does not display on the screen, until after the number for the power (in this case 2) is pressed."
That one is the circumflex accent, a zero width character intended to be placed as an accent above a second character, such as the letter i: î Î. There is a built-in list of characters which can accept the circumflex, and these when typed following option-i, will fit under the accent: â, ê, ô, û. If any other character is typed immediately following the following option-i, the zero-width circumflex is replaced with a non-zero width character (one that takes up space), and the typed character ˆfollows it.
Shift-6 is the carat ^,and is the one used as the 'to the power' operator.
Although your observations indicate that either will work in your situation, I'd suggest sticking with shift-6, the character originally assigned to this job, to avoid possible issues in transferring yur spreadsheets to another computer or a different application.
Regards,
Barry