Funny, I never thought of zooming in for speed check, didnt even know about it.
You know, bombing is still partly a feel thing. When making changes of direction into a tgt, I often guess the short or long drop based on a slight change of speed, has not failed yet for me. I made a few drops early on and came up short, but this was only due IMO, to not allowing for the change of speed from a change of direction.
I have been advised to use different delays etc, but found that at around 200-220 mph in a lanc, that a delay of 0.2 - 0.25 seconds for 1000 pounders is a minimum. The reason? Splash damage on buildings....and also that the spread will go roughly the width of the HQ or city you are bombing. I believe most people set their delay far too short. Another reason for this, is that a miscalculation on the run can be made up by having a longer impact spread...making the best of each run I suppose.
On the opposite side, if low level (100 - 200 feet) on FHs for example, a delay of 0.05 would be a maximum, as often the speed of the bomber is far higher in the last pull up / level / drop scenario.
I only aim to get above the ground ack...the 37mm stuff that is, any higher just makes for more time and less effectiveness.