95th percentile different to OpManager's?

Hi,

I'm a little confused by the 95th percentile watermarks in NFA5.5 and OpManager.

NFA says this:

Category Total Max Min Avg 95th Percentile
Traffic IN 7459.61 MB 6.14 Mbps - 984.76 Kbps 4.01 Mbps
Traffic OUT 7563.77 MB 5.25 Mbps - 998.51 Kbps 4.1 Mbps

For the same period on the same interface, OpManager says this:

Max (kbps) Min (kbps) Avg (kbps) Current (kbps) 95th Percentile (kbps)
In 4025.97 148.52 1022.03 539.81 863.35
Out 4124.0 74.83 1054.95 639.26 893.03

I can understand reasons for the discrepancies in average rates over this period, but why are the 95th percentile values so different? Do they mean different things to the two apps?

many thanks,
alec