difference between 90% testing & 99.9% testing
So why is it possible to only achieve 99% modeling quality/accuracy?
1:Backtesting on MetaTrader 4 assumes you will never experience slippage, which is certainly not true when trading live, especially with scalping EAs.
2:In MQL, MetaTrader 4’s programming language, the integral function start() which begins the data processing for every EA, only receives a tick if it has successfully processed the previous tick. Depending on the data and other factors, it’s not uncommon for an EA to skip ticks while backtesting.
3:Backtesting on MetaTrader 4 only permits the user a fixed spread. Most brokers now use a variable spread which can fluctuate by as much as 200% throughout a trading day.