Calculated item sum giving false number when added items not available

[tony_sat]

Hello, first post here, been a long time reader but now it´s time to give feedback to the community and ask for help also.

I have two items that added together give a third item: last(rx.ppscurrent)+last(tx.ppscurrent) = total.ppscurrent
The thing is that whenever I lost connection to the host I´m polling, the rx.ppscurrent&tx.ppscurrent become null values, hence the total.ppscurrent should be 0 or null, but instead it shows the last valid sum giving me false information. Example: last(rx.ppscurrent)=20 + last(tx.curent)=50 == total.ppscurrent=70, but if I lost connection to the host for 5 minutes, then during those 5 minuts the total.ppscurrent value is alwasy 70 (the last valid sum)

I now I have to make some check and validation of the info before doing the calculation, probably in the preprocessing tab of the calculated item, but not sure what should I check or how.

Any help would be appreciated!!

[tony_sat]

Hi splitek, than you very much for the info, I was able to solve it ust as you explained it, adding the count function to the expression. I will investigate the nodata() function as well, but for now is working just as expected.

Thanks!