
has to be four revolutions PER second.
The Big Bang Theory Season 10, Episode 20

Not under you PER se...
The Big Bang Theory Season 2, Episode 19

As PER your suggestion,
we're hanging out.
The Big Bang Theory Season 4, Episode 5

of 4.6 yoctometers
PER femtosecond.
The Big Bang Theory Season 5, Episode 18

Now, if you assume 15 tampons PER cycle
in a 28-day cycle...
The Big Bang Theory Season 1, Episode 4