as you have been advised on other similar queries you need to implement a storage of these metrics onto a table at a point in time - and then build your reports taking in consideration the point in time values vs the prior point in time.
and as also advised these counters reset if the instance is restarted (or failed over) so you have the further issue that any restart of server needs to be taken in consideration on your reports.
or buy something like SQL Monitor that does that for you.