Performance Equation for PI Manual Logger Data

Dear all, 

I am clueless on how to generate PE tag for this case:

Simply I would like to have a tag or PE tag that can total the value from 5 other tags which are not continuous from instrument data, but entered one by one using PI Manual Logger whenever the lab analysis test completed.

What parameters & settings do I have to specify in Performance Equation to achieve this so that it automatically totalize the values as we enter the data or keep updating until all 5 tags values are entered? see example below:

sample taken at 24:00 hours, analyzed, and data entered to PI below: 

Tagname ;  Value ; time entered into PI Manual Logger

Tag1    1  (entered now)

Tag2    2  (entered 10 minutes later) 

Tag3    3  (entered 1 hour later)

Tag4    4  (entered 1 hour later)

Tag5    5  (entered 30 minutes later)

PETagTotal  = (1+2+3+4+5) = 15

so at 24:00 hours, PETagTotal value is 15

Thank you for your inputs & help

Best regards,