Ratings plates for compressor

[NDG Elecs]

Just a quick query as to what an aspect of a rating plate refers too.
What is:
n/1 - value 2750

Piccy:

 

[davesparks]

My best guess would be rpm or another unit denoting rate of rotation.

 

[rsgaz]

RPM.

 

[Marvo]

The nominal RPM at no load and at the stated supply frequency.

 

[Lucien Nunes]

It's actually n/1' with the prime (') denoting minutes, i.e. "number per minute".

 

[NDG Elecs]

It's actually n/1' with the prime (') denoting minutes, i.e. "number per minute".

I thought there was an apostrophe on the plate but wasn't 100% sure so left it off the OP.
Thanks for the replies. It has been niggling at me for a little while!