I took the liberty of adapting saildog's picture (hope he doesn't mind) to add something I´ve fit to my lazyjack system after I experienced some difficulties in keeping it adjusted to a constant tension either while sailing or while at anchor with the boom raised:
I simply replaced a length of about 1 meter with shock cord!
This way I could discard the cleat system oftenly used to adjust lazy jack tension to the different situations.
I've seen to many guys forgetting to adjust their lazy jacks and either sailing with them over tensioned, thus interfeering with sail shape, or trying to put the sail down with the lazy jacks to loose and strugling to keep the sail on top of the boom...
In my boat the shock cord (which took a bit of experimentation to find the right length) does the trick for me, keeping the lazy jacks under just the right tension.
Regards!