"I share your frequently aired concern about HFT and flash crashes, and the fact that nothing seems to have been done to prevent a recurrence.

"I would just like to point out that a flash crash is not something that only happened once in 2010, and again in India a few days ago. If one looks at single US shares one finds quite a lot of them. See EPD and AGNC for example.

"These are so large that they in effect make it impossible for one to use stops at all. And they cause another problem. If one is using leveraged trades, as I do for tax reasons, a flash crash can cause a forced margin call across the board with huge resultant loss, unless one is very careful with leverage."

David Fuller's view Many thanks and I agree on all points, not least regarding leverage. However, we can still operate profitably in this environment but we should be conservative regarding leverage, which is probably a good idea in any event.