Creating a constant average line on a chart

[NikiG]

Hi,

I have an issue with trying to create a DAX measure that will return an average for a data column regarding number of services. My data is in one table so there are no relationships and there is a date hierarchy present. 

The data is very simple, each line item represents a single service transaction so there can be multiple services performed per day, month, year..etc.  

I am trying to create a process control chart (line chart) in relation to the number of services per day. Below I have shown the same data as the chart and as a table to aid understanding.

 As you can see the data visuals are correctly displaying the number of services on a given day, however, the mean (average) is not functioning correctly as i need this column to represent the average number of service per day. Hence, I need the DAX command to use the total number of services on a given day and return the average for this in the mean column. Essentially this will make the dark blue line representing the mean on the line chart above move to the mean (average) of the data set. 

The formula I am currently using for average calculation is the following:

Mean = CALCULATE(AVERAGE('Book (2)'[Service Count]))

Any help would be very much appreciated!

[lbendlin]

If you want to display the mean value per day then you need to calculate the mean value per day - in a new measure.