What is the MetaTrader SHIFT parameter?
The SHIFT parameter is used to identify a candle (or bar) on a MetaTrader price chart.
- The currently forming candle has a shift value of 0.
- The last fully formed candle has a shift value of 1.
- The candle formed before that one has a shift value of 2, and so and so on
So when you look at a MetaTrader price chart, the candle-shift-values read from 0 to N, from right to left. Where the candle with a shift of 0 (zero) is the candle at the far right edge of the chart.
This concept of a candle being identified by its shift-value runs deep in the MQL language.
Any of the 4 price values (High, Low, Open, Close) can be obtained using a shift value as an index to the built-in price series that are available in MQL.
- High : This is the high value of the currently forming candle.
- Close: This is the close value of the last fully formed candle.
- Open: This is the open price from 5 candles ago
The price series arrays only offer the price of a candle on the current chart (defined by its Symbol and Time-frame). MQL also offers functions to get the price value for a candle from any chart. These functions are named iHigh, iLow, iOpen and iClose.
The parameters for these functions are the symbol, timeframe and yes, of course, the shift:
|double iHigh(||string symbol, int timeframe, int shift)|
This will get you the high value of the last fully formed candle on a EURUSD 1 minute chart:
iHigh( “EURUSD”, PERIOD_H1, 1)
We’re almost done. Finally, every technical indicator provides a shift value as well, for the same reason.
For example, here is the RSI function:
|double iRSI(||string symbol, int timeframe, int period, int applied_price, int shift)|
To get the RSI value for the last candle, set the shift parameter to 1.
IMPORTANT note about shift of zero!
When you use a shift of zero, understand that the value can change on each incoming change in price (tick).
For example, for a candle, the only value that will not change for a shift of zero is the open price. The high and low values may change on each tick; and the close value does change on each tick.
Since nearly all indicators use the basic price values for their calculations, you can count on an indicator value changing on each tick if its shift parameter is zero.
WARNING: If you have logic that tests if an indicator value is greater or less than some value, and the shift is 0, the logic may be true for exactly 1 tick and then become false again. Generally, it is safer to use a shift of 1 to avoid this “bouncing”, but it can inject a delay in your EA. Look into the “Power Tab” on the Logic element to address these advanced situations.
Here is a forum post with more info: