Thanks for your responses. To be candid, I would have thought that even following 2 markets intensively in the general manner I described would be something of a challenge, let alone more.
For literally what you described, for genuine scalping, I agree with you, for the most part.
In forums generally (and perhaps in this one, in particular) people tend to use the word "scalping" very loosely, to describe any kind of "fast-moving (this term usually undefined) intraday trading". I appreciate, of course, that you're not one of them and meant scalping, when you said "scalping". So, technically I'm not a scalper, and probably shouldn't have replied in the first place - sorry.
I suppose it varies a little, according to the method, as you say: people whose set-ups don't materialise so often, and who have some way of "seeing them coming" (or at least being on the alert for them) can monitor more markets, can't they?
Example: a scalper who takes with-trend long trades (basing his entries on his precisely defined price action parameters, of course)
only when his MACD-line is
above both its midline and its signal-line ... when the latter condition isn't satisfied, he can perhaps keep tabs on a few additional markets, looking for an opportunity? (It's not how I trade, at all, but certainly there are people who do, and it could be a perfectly valid and reasonable
gescheft, for someone who likes that kind of thing?) In other words, they have an "intermittently disqualifying, overriding, directional bias indicator" which is itself much slower-moving although their trades, when the parameters are right for them, are very fast-moving. I'd venture to suggest that the number of markets they can reasonably hope to monitor would be roughly in
inverse proportion to the percentage of the time that their underlying directional bias indicator is fulfilled in each/most of those markets.
