Want to store variable value on an event
You need the calculation Aspect. In the calculation aspect you can define an event (Variable, Properties) and the Data (Variable, Properties) which you like to log.
You need to use the "Lab Data" Log Template Type and not Type "Direct"
For the calculation aspect you need the Calculation IT Extension. Of course you need the license for this extension ;-)
I am also using the logging with the calculation aspect for some event logging, works well.