The circle with the cross in it is a measuring point – generally it references bust point, waistline, or (in this case) bicep.
It also has numbers underneath that are *very* important – these numbers represent the **actual** measurement of the area in question. This doesn’t include wearing ease. This doesn’t include style ease (aka drape). This is the straight-up measurement.
That’s what this little bit of numbers means, and you need to know it. 🙂
Have a good day in sewing, folks!