This is the cumulative count of bytes received by this PM instance over the life of this bin. Because it accumulates for the entire life of the current, still-accumulating short interval bin rather than resetting every polling cycle, dividing it by the bin's Duration is how you'd reconstruct an average throughput figure for this exact port and window, as a check against the separate RxBytesPerSec gauge. For example, 112000000 bytes accumulated over this in-progress short-interval bin on a port provisioned for a 100 Mbps service would already show the circuit running well above its committed rate.