Forex Strategy Builder performs backtest of a strategy using historical bar data. It calculates each bar starting from the oldest one and finishes with the newest bar. The program interpolates every single bar using a special interpolation algorithm chosen by the user. The interpolation method serves to designate a route that the market price follows inside a bar.

FSB knows four facts about that route;

1. The interpolation starts from the Open price of the bar;
2. The route passes through the High price;
3. The route passes through the Low price;
4. The interpolation ends at the Close price;

FSB doesn't know:

1. Whether the price touches the High price before the Low price or in the opposite order;
2. Whether the price fluctuates up and down and passes through specific prices one time or several times.

We mark a bar “ambiguous” when the backtester cannot decide for sure in what sequence to execute the orders.