While we're on the topic, I'm curious. A lot of times you see performers as just plain understudies with no other role in the production, but they are not classified as standbys. Does that mean that they must always be present at the theatre?
Well if we're talking about straight plays, then I imagine they would not have to be present at the theatre but staying in the general vicinity. For musicals, they probably do have to be present at the theatre at least for Act I.
Dean: Can I tell you something?
Lorraine: That depends on what it is.
Dean: I think you're really really pretty.
Lorraine: (after a pause) Ok, you can tell me that.
When I was in the residant cast of the local Equity theater, we had to understudy the main stage productions. We had to call in at half hour before curtain and leave phone numbers where we could be reached. We were classified as understudies by Equity but did not have to be at the theater for each performance. These were Regional theater rules and must be different for Broadway.