To further support Grauhanens points earlier here is some data I collected this week with my Labradar. I chose 3 boxes from the same brick and tested each, different results for each box:
box 1
1124 fps avg MV
high 1142 low 1113
29.04 fps extreme spread
6.85 fps std dev
20 shot sample
box 2
1125 fps avg MV
high 1212 low 1107
104.72 extreme spread
14.56 Stf dev
50 shot sample
box 3
1124 fps avg MV
high 1166 low 1103
63.87 extreme spread
14.72 std dev
20 shot sample
box 1
1124 fps avg MV
high 1142 low 1113
29.04 fps extreme spread
6.85 fps std dev
20 shot sample
box 2
1125 fps avg MV
high 1212 low 1107
104.72 extreme spread
14.56 Stf dev
50 shot sample
box 3
1124 fps avg MV
high 1166 low 1103
63.87 extreme spread
14.72 std dev
20 shot sample