How can I keep a running total based on an attribute

I have an even in simulink that is assigned an attribute of a certain value (JobSize) and I want to keep track of a total sum of that value.

so if I have assigned JobSize values [8 6 10 8 12], I want to pull that attribute and keep a sum so that it will total [8 14 24 32 42] and can keep going. Also, samples are generated at random intervals, not on a regular basis.

Thanks

Chris