Conditional Format based on a Cell Reference

hi there. select the range you want to apply to (say from R37:T37)
go to Home tab -> Conditional Formatting -> New Rule -> Use a formula to determine which cells to format -> Format values where this formula is true:
=SUM($R$37:$T$37)=ROUND($O$37,1)

format the cells to the desired color.

next time though, do upload an excel sample so that we do not have to manually key in your data to do a testing.

input the desired results so that we don't have to second-guess if what we are doing is correct or not. you may look at my signature to upload an eg that is easier to understand.

the upload attachment must be done by going to Go Advanced. click on Manage Attachments. Choose file, upload and close the window.

if i really guessed it wrongly, please upload something according to my recommendations. try to use the solution i have given and we'll help to advise what went wrong.

remove all your previous conditions. select the range you want to apply to (say from R11:T740)
go to Home tab -> Conditional Formatting -> New Rule -> Use a formula to determine which cells to format -> Format values where this formula is true:
=AND(SUM($R11:$T12)=ROUND($O11,1),$O11<>0)

i am fixing the columns to reference to, but not the rows. that is so that it can be applicable for all the rows you need.

when you say "original" formula, do you mean mine or the one you amended? with my formula:
=SUM($R$37:$T$37)=ROUND($O$37,1)
i fixed all the columns and rows, so it will always compare the same cells. it was based on your description and i lazily fixed everything since that is the 1st option when you press the F4 key. if you don't know this, you can actually press F4 to add dollar signs to your cell reference when you are doing formulas. for eg, type in cell A1:
=b10
press F4 and you'll see:
=$B$10
press F4 again and you'll have:
=B$10
and it goes on for a total of 4 different variations.

if you are talking about the formula you used:
=IF(O37=0,,SUM(R37:T37)=ROUND(O37,1))
i actually talk about this in my Excel training classes. but it'll be harder here without the visuals. try and imagine conditional formatting working behind the cells.
1. i mentioned to select from cell R11. forgot to underline it in my previous post but this is very important.
2. when you get to the New Formatting Rule window via Home tab -> Conditional Formatting -> New Rule -> Use a formula to determine which cells to format, notice that it requires just a single formula.

now, the formula you placed in point 2 will be placed in the cell you selected in point 1 (in the backend). you can do a simulation in cell AB11 for eg. simply type the formula you used:
=IF(O11=0,,SUM(R11:T12)=ROUND(O11,1))
so imagine this cell is actually R2. the conditional formatting drags this formula across and below (R11:T740). in our simulation, just drag across to AD11 and below to AD14.
you will see a bunch of TRUEs, FALSEs, and 0s. the TRUEs will format the cell. FALSEs and 0s will not. why did AC11 become FALSE? if you did not fix the cells, dragging the formula from AB11 to AC11 will change the cell referencing. you are now comparing if P11 (wrong cell) equals 0, put 0. otherwise, check if sum of S11:U11 (wrong cells) is equals to rounding to 1 decimal of P11 (wrong cell).

you could still use the IF formula though. i just didn't see a need. all the conditional formatting requires is TRUE or FALSE. but if you fix the columns, it still works:
=IF($O11=0,,SUM($R11:$T12)=ROUND($O11,1))

by the way, don't merge cells if unnecessary. in your case, it just seems like you need the row a little wider. simply adjust the row height.

hope that helps.