Power Cycle Calculations Help

Trying to understand a power study done a few years back on one of our lines. It says there were volatge sags on one phase (277) that went as low as 244 and lasted a range of 1/4 cycle to 1 millisecond?

If I understand correctly on 60Hz power that 60 times a second and one cycle is 1/60th of a second which would be 16.6 milliseconds per cycle correct? Which would make a quarter cycle 4.15ms?

So it lasted 1ms to 4.15ms?

Seems as if they would have worded it differently - 1 mSec to 1/4 cycle (from lowest to highest). Or, even 1 mSec to 4 mSec.
Maybe you could contact the reporting person and ask?

I primarily need to know if I am understanding this correctly and if my math is correct.

Yes, I believe you not only understand it but your math is indeed correct.

I'm not really a power guy but it seems odd to apply an RMS value to an event that doesn't last at least a full cycle. Is that normal? I've never had a power analysis done.

Keith