On uses and abuses of e-mini trading systems - abuses
Let us start from the abuses. If only because they are more common.
In the business as badly dominated by marketers and other phonies masquerading as traders as the business of e-mini day trading is, it is hard not to run into some abuses of trading systems. The simplest of them is in abusing the very term "system."
This term implies, or at least that is how it is understood by people serious about developing trading systems, that a trading method or strategy (these terms are pretty much interchangeable and are used that way in this article) you call the system has been systematically examined, usually over a period of few months, at the very least, and that a respectable statistics has been generated to demonstrate the effectiveness of trading strategy in question.
To do so in a way that can be acceptable, one should insist that the strategy that one tries elevate to the status of the trading system is objective, meaning that it can be executed in the same, at least in principle, way by all traders using it. In other words, no trader's discretion (or extra skill) should be required to trade it properly and successfully. Now, if the strategy is discretionary and hence its results depend on the trader's skill, it obviously cannot be objective.
Because of that examining it in the way that does not raise objections (or gives rise) to possible abuses of manipulating the data to produce the best results is very hard if not impossible. And if this cannot be done objectively, you are likely to end up with systematic errors. It is a very poor reason to call something "system" just because it is likely to have systematic errors. It is actually a very good reason not call something like that "system."
Unfortunately, the very term "system," the very concept of the system, seem to imply the picture of superiority and completeness than its poor cousins "strategy" and "method" just sadly cannot even begin to muster. It is largely for this reason, or so I suspect, that the term "system" is much more preferred by various marketing hacks masquerading as "system developers." It simply seems so much more glamorous and inspiring so much more confidence than similar terms that should be used instead and much more appropriately too.
The trading system, whether it is a stock or Forex or futures trading system, should be objective. If it is not, the person marketing it cannot be taken seriously as a developer and is better to be avoided. Why would you want to deal with someone who either has no clue what the proper trading system is or, even worse, he does and purposely calls it "system" even though that term should be reserved for something else?
The proper term in a case like that is "trading strategy" or "trading method." A collection of such methods is what one could rightly call "methodology." There is nothing wrong with these terms at all. There is plenty of room for strategies or methods in trading that have not been systematically examined for their best, most effective use requires relying on trader's discretion.
An excellent example of a purely discretionary e-mini day trading methodology that should get you well prepared for trading e-mini futures is KING.