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    User name R. Michaels

    Log entry time 10:15:46 on January31,2009

    Entry number 258455

    keyword=neg. BB dtime, switched to L-HRS scalers (datamon)

    The datamon GUI was showing negative deadtime at the start of
    each run. Alexandre Deur tells me this has been happening for
    a long time (weeks). I suppose it's because the BB scalers are
    not gated properly at the start of a run, though I would have
    guessed that would cause larger positive deadtime (artificially,
    not really). I've switched to L-HRS scalers. Those are gated
    correctly by start-of-run. We had switched away from L-scalers
    a few weeks ago when there was double-pulsing on L1A, but this
    was fixed some time ago. (And why BB are not gated properly ?
    Ask any expert, it was a deliberate decision.)

    BTW, we also get "negative deadtime" during beam trips, but this
    is because the code tries to estimate how many data should seen,
    so if prescale factors are high and the rates are unstable you
    can get an artificial negative. Do not panic.