The Average Block lets you convert instantaneous measurement into time-averaged measurements. The block is simple to use - put in the new value in ‘New Value’ drawer, and get the running average in the ‘Average’ output. You can choose how many time points to average - 10, 20, 50, 100, 200, 500 or 1000.
See the attached sample .rbt file, which displays time-averaged sound level on the NXT screen.