How to figure MTBF with variable number of machines

[wsj81383]

I need to do Weekly and monthly Mean Time Between Failure calculations for our service organization. We use an Access 2000 based db and I pull the call dates, downtime hours , machine serial numbers etc. from various tables. It is easy to write a formula to give me MTBF values using the machines that have had open calls made during a specified time period. However I need to calculate the total number of machines that were in the US during each week (using install dates) represented in the report as we are installing a lot of machines. The trick is to get Crystal reports to figure out how many machines were in the U.S. during the first week of December, second week, and so on while calculating the number of calls for each week at the same time. I usually end up with an error referring to calculating something that refers to another calculation. Any ideas would be appreciated.

 

[synapsevampire]

If these are different tables, and don't have a reasonable means of joining them to present all of the data you need, consider using a subreport at the Week Group level to show the numbers for the installs.

-k

http://www.informeddatadecisions.com

kai@informeddatadecisions.com

 

[wsj81383]

Thanks, SynapseVampire, I tried doing a subreport earlier but I don't know how to pull the totals of the install dtaes in the subreport back to my MTBF calcs in the main report. They need to be in the main report's formula.