See the SPL Test Setup.

All published SPL measurements are taken from the middle SPL meter. The different meters have different "attack" and "decay" times, hence the varying levels at any moment in time.

If any of my neighbors are interested, I'll provide them with a CDR containing the actual video these screen captures were made from. During playback, there is a direct cause and effect between the sound of playground noise on the video and the high SPL readings. A few of the pictures show a "LO" level. This is what the meters read when there is a temporary lull in the playground noise, or during the times when there is no playground usage.