Need Help understanding the Menu on my Mods

G'day all,
I have an Ijoy E-Top Mod as well as a Sigelei Mini Zmax as well as a Vnew mod which seems to be a clone of the Vammo.
I understand all the menu's but one. Can some one please tell me what "EMS,RMS and "MEAN" settings do?
I have tried to google these and cannot find an answer.

Thank you in advance
Huon.

 

It has to do with the way it "pulses" the volts to the atty. I'm not that tech savvy on the subject, but that's the jist of it since nobody else answered.
IIRC, I used to use RMS... it's also the reason a lot of people prefer mechanicals since it's a quick, constant fire instead of pulsing the volts intermittently.

_