What definable positions do these "marshalls" actually hold ??

I counted 11 vestys at Braddan in total and surely they must all have different jobs.

Doctors, nurses, blood transfusion lab technicians, concrete dust layers, flag men, and of course a marshall or two ????

I would like to know how a group like this is put together and why so many are needed at these selected spots........

A similar number was at Ballacraine last year (I have a photo) and it appears that there are some sections with a lot of people in fluorescent vests, and at other places we see only two.