Change your \ to a / if you want to do division.

As far as I know, \ has no meaning in LTSpice, so it's not surprising it gives an error message about something being "unknown" when you use this symbol.

Change your \ to a / if you want to do division.

As far as I know, \ has no meaning in LTSpice, so it's not surprising it gives an error message about something being "unknown" when you use this symbol.

Edit

Based on comments, the actual problem is that the expression must be surrounded by { and }.