Re: How to calculate the open time of a Service call in Service Desk 4.5 SP17
If you mean a field that will tell you how long a Service Call has been opened for, the calculation is actually pretty simple but AFAIK, Service Desk Calculated Fields will not update until after you change the status to closed. You cannot access Calculated Fields from Business Logic Rules for direct manipulation either.
My guess is you can use an External Update Rule and have a webserver do the calculation and return the value to Service Desk, although I think it'd be somewhat time-consuming to open a Service Call run the calculation every time. If the user really really needs to know, I'd use a button to trigger the rule.