conditional formatting - detect duplicate cell values

[jimqc]

The response I got yesterday [=IF(COUNTIF($A$3:$A$15,A3)>1,TRUE,FALSE)] was helpful but not exactly what I was looking for. My problem is I'm not comparing consecutive cells ($A$3:$A$15,A3). I want to compare ($A$3;$A$5;$A$7;$A$9;$A$11;$A$13;$A$15,A3) and($A$2;$A$4;$A$6;$A$8;$A$10;$A$12;$A$14,A2), but when I enter the formula this way it doesn't work. What am I doing wrong?
Thanks in advance for any help,
Jim