Metric expression for delta from startTime and endTime

Hi, I have a Counter for processed logs. I also have a table in Grafana where I would like to show the changes of this counter during the selected time range from the dropdown.
E.G. If the selected time range is: Last 1 hour the value which is showed should be: currentCounterValue-oneHourAgoCounterValue`` .How can I achieve that?
I tried a lot of expressions and reduce functions but still nothing work.