# periodOverPeriodDifference


The `periodOverPeriodDifference` function calculates the difference of a measure over two different time periods as specified by period granularity and offset. Unlike a difference calculation, this function uses a date-based offset instead of a fixed sized offset. This ensures that only the correct dates are compared, even if data points are missing in the dataset.

## Syntax


```
periodOverPeriodDifference(
	measure, 
	date, 
	period, 
	offset)
```

## Arguments


 *measure*   
An aggregated measure that you want to perform the periodOverPeriod calculation on.

 *dateTime*   
The Date dimension over which we are computing Period-Over-Period calculations.

 *period*   
(Optional) The time period across which you're computing the computation. Granularity of `YEAR` means `YearToDate` computation, `Quarter` means `QuarterToDate`, and so on. Valid granularities include `YEAR`, `QUARTER`, `MONTH`, `WEEK`, `DAY`, `HOUR`, `MINUTE`, and `SECONDS`.  
The defaults value is the visual date dimension granularity.

 *offset*   
(Optional) The offset can be a positive or negative integer representing the prior time period (specified by period) that you want to compare against. For instance, period of a quarter with offset 1 means comparing against the previous quarter.  
The default value is 1.

## Example


The following example uses a calculated field `PeriodOverPeriod` to display the sales amount difference of yesterday

```
periodOverPeriodDifference(sum(Sales), {Order Date})
```

![\[This is an image of the return of the example calculation.\]](http://docs.amazonaws.cn/en_us/quick/latest/userguide/images/MonthOverMonthDifference.png)


The following example uses a calculated field `PeriodOverPeriod` to display the sales amount difference of previous 2 months. Below example is comparing sales of `Mar2020` with `Jan2020`.

```
periodOverPeriodDifference(sum(Sales),{Order Date}, MONTH, 1)
```

![\[This is an image of the return of the example calculation.\]](http://docs.amazonaws.cn/en_us/quick/latest/userguide/images/MonthOverMonthDifference2.png)