Learning about the anemometer

I’m curious what kind of numbers you might expect to see here.

80% natural gas furnace in the unconditioned 40 degree attic
this is the closest register by straight line.
i’m just messing around, i’m not doing an inspection

How does the anemometer know what the dimensions of the register are? 60 cfm is on the display. For that meter to know the cfm it would need to multiply the measured velocity by the area of the register opening.

Here is a link to info about typical air flow rates for HVAC

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thank you sir

The anemometer is displaying the air flow across the sensor area, not the entire register. You can extrapolate that information by knowing the area of the register opening and the sensor opening.