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Im trying to figure out how the NormalizeDouble function works. Can someone see what i do wrong here? The returned value from line 3 and 4 from the NormalizeDouble function is 0 instead of a rounded number as expected.. 


double SLBuyLevel = Low[1]-20*Point;
 double SLBuyDif = Close[1]-SLBuyLevel;
 double SLInPoints = NormalizeDouble(SLBuyDif*Point,Digits);
 double SLDifInPips = NormalizeDouble(SLInPoints*Point);
 

  1. SLBuyLevel is a price. SLBuyDif is the difference in prices (0.00123).

  2. PIP, Point, or Tick are all different in general.
              What is a TICK? - MQL4 programming forum 2014.08.03

    Multiplying by Point does not give you PIPs. It doesn't give you a difference in points either. 0.00123 ÷ _Point = 123 the price difference in points. Compute what a PIP is and use it, not points.
              How to manage JPY pairs with parameters? - MQL4 programming forum
              Slippage defined in index points - Currency Pairs - Expert Advisors and Automated Trading - MQL5 programming forum

  3. You used NormalizeDouble, It's use is usually wrong, as it is in your case.

    1. Floating point has infinite number of decimals, it's your not understanding floating point and that some numbers can't be represented exactly. (like 1/10.)
                Double-precision floating-point format - Wikipedia, the free encyclopedia

      See also The == operand. - MQL4 programming forum

    2. Print out your values to the precision you want with DoubleToString - Conversion Functions - MQL4 Reference.

    3. SL/TP (stops) need to be normalized to tick size (not Point) — code fails on metals. (On 5Digit Broker Stops are only allowed to be placed on full pip values. How to find out in mql? - MQL4 programming forum) and abide by the limits Requirements and Limitations in Making Trades - Appendixes - MQL4 Tutorial and that requires understanding floating point equality Can price != price ? - MQL4 programming forum

    4. Open price for pending orders need to be adjusted. On Currencies, Point == TickSize, so you will get the same answer, but it won't work on Metals. So do it right: Trailing Bar Entry EA - MQL4 programming forum or Bid/Ask: (No Need) to use NormalizeDouble in OrderSend - MQL4 programming forum

    5. Lot size must also be adjusted to a multiple of LotStep and check against min and max. If that is not a power of 1/10 then NormalizeDouble is wrong. Do it right.

    6. MathRound() and NormalizeDouble() are rounding in a different way. Make it explicit.
                MT4:NormalizeDouble - MQL5 programming forum
                How to Normalize - Expert Advisors and Automated Trading - MQL5 programming forum

    7. Prices you get from the terminal are already normalized.

    8. PIP, Point, or Tick are all different in general.
                What is a TICK? - MQL4 programming forum 2014.08.03

 
William Roeder:

  1. SLBuyLevel is a price. SLBuyDif is the difference in prices (0.00123).

  2. PIP, Point, or Tick are all different in general.
              What is a TICK? - MQL4 programming forum 2014.08.03

    Multiplying by Point does not give you PIPs. It doesn't give you a difference in points either. 0.00123 ÷ _Point = 123 the price difference in points. Compute what a PIP is and use it, not points.
              How to manage JPY pairs with parameters? - MQL4 programming forum
              Slippage defined in index points - Currency Pairs - Expert Advisors and Automated Trading - MQL5 programming forum

  3. You used NormalizeDouble, It's use is usually wrong, as it is in your case.

    1. Floating point has infinite number of decimals, it's your not understanding floating point and that some numbers can't be represented exactly. (like 1/10.)
                Double-precision floating-point format - Wikipedia, the free encyclopedia

      See also The == operand. - MQL4 programming forum

    2. Print out your values to the precision you want with DoubleToString - Conversion Functions - MQL4 Reference.

    3. SL/TP (stops) need to be normalized to tick size (not Point) — code fails on metals. (On 5Digit Broker Stops are only allowed to be placed on full pip values. How to find out in mql? - MQL4 programming forum) and abide by the limits Requirements and Limitations in Making Trades - Appendixes - MQL4 Tutorial and that requires understanding floating point equality Can price != price ? - MQL4 programming forum

    4. Open price for pending orders need to be adjusted. On Currencies, Point == TickSize, so you will get the same answer, but it won't work on Metals. So do it right: Trailing Bar Entry EA - MQL4 programming forum or Bid/Ask: (No Need) to use NormalizeDouble in OrderSend - MQL4 programming forum

    5. Lot size must also be adjusted to a multiple of LotStep and check against min and max. If that is not a power of 1/10 then NormalizeDouble is wrong. Do it right.

    6. MathRound() and NormalizeDouble() are rounding in a different way. Make it explicit.
                MT4:NormalizeDouble - MQL5 programming forum
                How to Normalize - Expert Advisors and Automated Trading - MQL5 programming forum

    7. Prices you get from the terminal are already normalized.

    8. PIP, Point, or Tick are all different in general.
                What is a TICK? - MQL4 programming forum 2014.08.03

wow, thank you so much. Will look into all your inputs.. 

 
What would be the cleanest way of calculating the difference between two prices in pips or points? Taking into account that metals and JPY crosses have different digits and that the pip size is calculated differently than other forex pairs?   
 

PIPs have no meaning in metals, use TickSize.

What part of #1.2 was unclear? SizeInX = (priceA - priceB) ÷ X

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