If you are two close to the chrono you can get odd results due to the arrow flexing.
I found going back a couple of paces helped get more consistent results.
But if yur readings are consistent then they are probably true, are you shooting heavy arrows?
Here are some of my speeds.
I took my little crossbow pistol as a reference as it is easy to shoot accurately and consistently.
I'm shooting in my garage and I had to build a lighting rig for it.
Chronometer Arrow/bolt speed Results Fps max relaiable mph
10/1/2010 Bowpistol 132 90
10/1 Hazel bow 136.4 93
11/1 Longbow light arrow as per Hazel bow 169.7 115.7
11/1 Longbow heavier 11/32” arrow ~166
29/1 1hr bow rawhide backed 44lb@28" 152.3
I think these figures are reasonable...but worry about 'em won't change 'em anyhow
Hope that's useful.
Del