Good question. I'm unable to find the answer either. I've posted this at Socialcast (an awesome tool for group discussion). If I hear an answer, I'd share it here.
I've added 2 charts comparing the value. Latency is _always_ higher than Ready. So I'd track Latency instead of Ready. Even if I go back 7 days, there is never a time where Ready was higher than Latency. I'm using VC Ops 5.6 for the chart.