A gauge is the one amCharts chart whose reading is not in a series at
all: the needle is an AxisBullet on an axis data
item, so the chart commonly carries zero series. MAIDR reads it from the
chart instead.
"73" on its own is not a reading. The announcement carries the dial's ends and the band the needle landed in, because neither is written anywhere a screen reader can reach on a drawn gauge. The tone is pitched against the range rather than against the value, so where the needle sits on the dial is what you hear.