There is not conditioning option dependent on a cell other than itself.
However you can use an IF Funtion to set the cells value.

=IF(A2=1,"False","True")

The above funtion will return a value of false if and only if A2 equals 1,
Else value is set to False
There for if the Target cell does not equal exactly 1, the response is true.

"Justin Larson" wrote:

I am trying to apply a conditional formatting rule that would return a true
if the cell immediately to the left does not have a value exactly 1 less than
the value of "this cell."

My problem is that I can't find a function or reference operator for "this
cell" when applied to an entire column.

ie-
A B C
1
2 5 6 True
3 12 13 True
4 6 5 False
5 7 9 False

Conditional formatting applied to column B.

I looked at offset, but I need an absolute cell reference to offset from,
and I don't have that.

Thanks in advance