Standby Vs. Understudy??

#1Standby Vs. Understudy??

So what is the difference between being a standby and being an understudy? Are standbys required to be at every show? Are tehy "guaranteed" any number of performances? Are standbys contracted under Actor's Equity like any other performer in a show? What would a standby's payscale be compared to that of an ensemble member or a swing or an understudy? What are the chances of a standby getting "promoted" to taking over the role he/she covers?