which Oxygen sensor is #2 ??

I got the code 1213 Oxygen sensor #2 lean/rich control stop (DME 3.3. only)
and I have the sensor already.
which one is #2 (or which is #1) ???
95 530i manual trans. M60 engine has 2 sensors.

Thanks

you should replace O2 sensors in pairs, so get another one!

should be the left but i would not replace just one, it's ok to do just the front sensors on a obdII car (4 sensors total) and not replace the back sensors but i wouldn't want to do a left or right primary only. a control limit code may or may not be a bad sensor, you may have a intake leak causeing a mixture problem on that bank and the computer threw the code because it's at it's adjustment limit, or that sensor is worn out and out of range and is throwing off the mixture on it's own

i wonder how many V8 people replaced the sensors and still got the O2 codes, I read about 3 or 4 over the past couple years.

Thanks for reply(s):
On this particular case:
Changing one (#2)=driver side got rid of the check engine light; and went for the smog re-test; this time pass !!!!
with flying colors;
upon comparing the emission numbers; they were all reduced and by a lot.
(meet the tough Californis standars)

Thanks again to all