We calculate request response times of our application by a calculated value:

requests.total_processing_time:
=> sum of all request processing times
=> Store value : Delta (Simple change)

requests.count: count of all requests
=> sum of all request processing times
=> Store value : Delta (Simple change)

Expression:

last("requests.total_processing_time") / 
( 
   last("requests.count") + 
   count("requests.count",#1,0) 
)

We added the expression 'count("requests.count",#1,0)' to prevent a division by zero.
Otherwise, Zabbix alters the calculated item to "unsupported" if at least one item is not available or a division by zero appears and reactivates the item after the configured value for "Refresh unsupported items".
(Administration => General => Other)
We do not want to increase this value only for reactivating calculated items faster.

From our point of view a adeuqate solution might be:
A option "skip on calculation problems" which just skips the calculation if a division by zero appears of a item is not available.
No value will be stored - the user should see a measurement hole.

Why do we not calculate the performance measure in the application?
Adding values to requests.total_processing_time and requests.count is very useful, because :

• the measurement frequency of these value can be changed without changing the application
• the calculated/displayed values are standardized and not depended to the measuement frequency
• the application code for requests.total_processing_time and requests.count can be very simple from locking and queueing point of view