"Once every second" vs. "Once per second" vs. "Once each second. "

Question

I wonder which form(s) are correct amongst the following:

• Once every second
• Once per second
• Once each second

Example of use:

You may only do something once per second.

Answer 1

Once per second is the most obvious. Once each second is probably the least obvious, but it's perfectly understandable. Once every second can be used if you want to make a particular emphasis because it's not a single syllable, so you wouldn't use it when rattling off some data and mentioning a rate.

But if you were saying that a particular bottling facility was making a remarkable amount of plastic bottles that pollute the environment, you could use "every" to put an emphasis on the fact that it never stops. This plant never stops! It just keeps running, day and night! It makes an entire truckload of bottles that will wind up in the river once every second! Don't overuse it.

In spoken English, you'll also hear, "Once a second," but this is never really used in writing unless you are precisely transcribing casual speech. I don't think there's any good reason for this. The spoken language just isn't exactly the same as the way it is written.