http://bbs.168p.net/attachments/month_0704/20070405_4037ee6784819812ff59Qyr4bNRSbs4x.jpg

From this image, we can see :
1. AT900-T
everage BP = 301mm
Sigma = 3mm
=>
66.7%: 304 ~ 298 mm
95% 307 ~ 295 mm
99.96% 310 ~ 292 mm

2. AT900-P
everage BP = 315mm
Sigma = 3mm
=>
66.7% 312~318mm
95% 309~321mm
99.96% 306~324mm

Therefore, if you want a head-heavy AT900-T, Just look for the 15% ones.
So do those who want head-light AT900-P.

AT900-Ts can be more head-heavy is you spend some time picking it from the lots.

This is based on the assumption of normal distribution which can be applied in most productions. If the assumption changed to uniform distribution, there will be higher chance to get a head-heavy AT900-T.

waoh what.. wow ... data... brings back ... memories.. ?