Calculate constant result

[user900]

I have a table with report date, ID and test result (pass or fail).  There is a new data table received each month.  For the first month, I have 185 failed results.  For the second month, I have 200 failed results.  I'm using a line chart to trend the results by month but when the new month's data is received, my data point changes to 385 which is cummulative.  I need to show the historical data point as it was in the first month (185) and the new month (200) How should I do this?  I have very minimal BI experience.

Thanks in advance

~user 900

[kpost]

Please show screenshot of the chart, and the measure(s) you are including in the chart.

Is this data all being combined into one table?  Is it in two tables?  If it is in two tables do you have a Date Table with relationships to both?  etc etc....

[user900]

Repeat should represent those who failed since May which is when we started measuring.

[user900]

Data is combined into one table with a relationship to a date table

Measure is: 

Result:

I need June to show 185 and July to show 200.  If I get this right, my % should fix itself.