Never having been involved with things that go bang, apart from lugging them about from time to time (in which case you very much hope that they don't), how does a 1/2 lb smoke bomb work? Does it emit smoke upon release so that you can follow its trajectory, or merely on impact so that you can see where that is?
Evidently the practise bombing in the 1920s at Bicester (a uniquely preserved pre WWII RAF station) was done over the grass airfield, which was marked with an aiming point. The ""bombs" were simulated by the firing of flash bulbs in the Sidestrands, etc. By also releasing stannic chloride from containers made out of Tate & Lyle Golden Syrup tins, the resultant cloud could be tracked from a "Camera Obscura" in the roof of SHQ and the drop wind assessed. Thus an optimum release point was calculated and the difference between that and where the flash bulb firing occurred created the theoretical error, to be reported back to the crew after landing and/or their boss!
No doubt we will soon have to return to the use of Syrup tins and Flash Bulbs as Mr Osborne seeks out further efficiencies....