This is the average fan speed recorded for this fan over the sampling interval that produced this specific archived history row. Because it's archived rather than live, an admin can pull a series of these HistSpeedAvg values across many rows to build a trend line of the fan's typical speed over the past several hours or days, useful for spotting a slow degradation that a single live reading wouldn't reveal. A gradually declining HistSpeedAvg across successive history rows, even while HistSpeedMax stays roughly constant, can indicate the fan is having to work harder to reach peak speed.