Don't have the video in from of me, but I think he is referring to obtaining target speed, have a look at this, it is from SH3 but similar principle:
http://www.paulwasserman.net/SHIII/#Step%204:%20Wait%203%20Minutes%20Then%20Make%20Ne xt%20Observation%20(DS)
Edit: There is also another great guide SH4, Hitman's 100% Manual Targetting Guide, it is available in print format.
RDP