Conditional formatting based on multiple text criteria

I'm trying to set up conditional formatting in a spreadsheet where there are 3 possible correct letters that can be entered into a range of cells and if one of these letters is not entered then I would like the cell to be highlighted.

To be more precise, it's an accommodation spreadsheet and in each cell if someone needs a room for that particular night (each night is represented by a separate column) then a letter is used to indicate what type of room they require i.e. "k" is a king room, "s" is a Suite and "t" is a twin. I don't want to force people to have to select from a list which would be the obvious solution to this as it is simply too cumbersome for the amount of data entry we do.

However i want to ensure that if someone accidentally enters anything other than t,k or s then the cell is highlighted. We work in large spreadsheets covering months of dates so to manually have to find any errors is hugely time consuming.

I've tried setting up OR formulas and NOT formulas but can't seem to find a solution.

Hi,

Is this what you're after? Try typing anywhere inside the bordered cells...

I hope this helps

@FDibbins: great idea, I didn't think of that

Hi there

Yes, that's exactly what I'm looking for but for some reason I can't make it work in my spreadsheet for some reason.

I've copied the formula over into the conditional formula building tool but it's not working correctly. Are you able to please explain the exact steps maybe?

I'm attaching my spreadsheet for ease of reference.

Many thanks

Tanya

I'm obviously missing something very basic but am not able to make either solution work and it's probably to do with my lack of understanding of the main cell ref being B2 maybe?

@ajryan88 when I copy your formula into the conditional formatting builder tool it works in certain cells but not in others and I can't pinpoint why.

@fdbibbins your solution seems to be exactly what i'm looking for but when I enter it via validation it will either continue to let me enter whatever I like into the cells or won't allow any valid entry at all including the T, S and K

Any suggestions on where I'm going wrong?

All help much appreciated.

The first cell range I'm trying to make this work for is S8:CJ27

Thanks

That's great :-)

Thanks so much - I really appreciate your help.

Kind regards

Tanya