My results are different when I retest using the same configuration. How is this possible?

Even with an unchanged indicator configuration, several other factors can contribute to inconsistent results. The total profit figure is usually affected more than other criteria such as the win rate or the total number of trades, etc. This is because these "other" factors are more likely to change the gain/loss values than the trade entry points, so they will usually affect only values such as the profit or ROI. A change in the historical data, on the other hand, will change results such as the number of Take-Profit hits, Win Rate, Chalkups, etc. as well as gain/loss values.

The main reasons for gain/loss values to change are as follows:

• First, a variation in spreads. Make sure you don't have the "Current" option in the spread selected. This will cause different results while the market is open and inconsistent results while the market is closed, as most brokers leave a very high spread over the weekend. Instead, select one of the fixed spread values, such as 50 or 30.
  
  
• Second, a change in the historical data. This will affect results not only in backtesting (manual or automatic) but also during forward testing or live trading. A change in historical data happens when there is a change in the broker server, and it can also occur when there is a change in the type of account (e.g. if you switch from a demo account to a real account). If you see changes in results such as the number of Take-Profit hits, Win Rate, Chalkups, etc., this is the likely cause.
  
  
• The margin calculation can also affect the result, though to a much smaller degree than a variation in spread. Note that as market prices change, your base currency price will vary over time. You will notice this difference in backtests that involve the pairs outside the Major ones (if you are using the USD and the same principle is applicable if your account currency is another one).
  This is true for manual or automatic backtesting.
  
  
• Swaps and commissions may also vary over time, depending on your Metatrader account. The NNFX Algo Tester uses the current value of swaps and not the historical values, since swap rates are not included in the historical data. This information is provided by your broker.