Graph load avg of apps by log files

[sivann]

Application logs various time-consuming steps in syslog file as "step x time elapsed: y" where y is seconds.

I would like to have a graph similar to load average which shows for each minute how much cpu time was dedicated to that step. What I tried:

1) Created Log item, to parse logfile and get latest value (works fine)
2) Created calculated item which gets last() value from Log[] item and graphs last value (works fine)
3) Created a calculated item to calculate 100 * sum(of last 60 seconds of values)/60 (does not work)

3a) I've tried the following formulas for calculated item:
100 * sum("log[/var/log/mylog.log,\"blablah, elapsed=([0-9]+)\",,,,\1]",60) / 60

Result: Unsupported item with error: Cannot evaluate function "sum(60)".

3b) To cope for missing values on the sum() I tried to also use nodata:
nodata(log[/var/log/mylog.log,\"blablah, elapsed=([0-9]+)\",,,,\1]",60) or
sum("log[/var/log/mylog.log,\"blablah, elapsed=([0-9]+)\",,,,\1]",60) * 100 / 60

Result:
Cannot evaluate function "nodata(\"blablah, elapsed[0-9]+)": item "myhostname:log[/var/log/mylog.log" does not exist.

I'm out of ideas