Oh I think I found it (thanks Google).
Zone 1 – 60-70% of threshold heart rate (easy pace, walking)
Zone 2 – 70-80% of threshold heart rate (easy, slow jogging)
Zone 3 – 80-90% of threshold heart rate (tempo pace, getting quicker)
Zone 4 – 90-100% of threshold heart rate (fast pace, hard effort)
Zone 5 – 100-110% of threshold heart rate (race pace, extremely hard)
My watch does measure my HR, but I've never set my maximum, so although I do look at what the rate is, I've never used it for my training. I've had the watch that measures HR less than a year so am used to running on feel.
I think I do most solo runs in 3, club group run in 2 (cos we're chatting), 4 or 5 for interval training.
I'm curious now, it will be easy enough for me to see its rate when I was doing hard hill training, which will be my max I guess.
I know when I was marathon training I needed to slow my natural pace down so I could improve my endurance. I didn't enjoy it.
I sometimes try and run at "I don't want my hair to get sweaty so I need to wash it pace"!