|The following should get you just the updated number, or|
do you want the whole line?
Anyway, change 'set logfile=logfile' to equal your actual
for /f "usebackq tokens=1* delims=," %%a in (`findstr /i /c:"Error  WDC Plot: Outgoing Data Last half hour, Avg Val" "%logfile%"`) do (
for %%c in (%%b) do set AvgVal=%%c