Monitoring windows services across hosts

[Tractorboy]

I need to monitor windows services across multiple hosts and alert if zero or more that one service of the same name is running

host A - Service A
host B - Service A
host C - Service A

I am happy with grpsum but with a slight issue as the service may not be installed on all of the hosts, and therefore the vaue becomes +255.

Has anyone any ideas how to get around this? I'd prefer not to have to lock the monitoring to only install hosts.

Thanks

[Tractorboy]

A Solution

I have found that if I add a calculated Item testing the key against 0 then a true (1)/ false(0) is returned.

I should now be able to grpsum these and trigger on <>1.