Thanks James- yes you are correct that my batteries were low- so we now know one one useful LED code: “3 quick flashes, pause 1 second, 3 quick flashes…” indicates dead batteries.
Not sure why my batteries were low though- I’ve only had this meter for a month and not much use because of the VDC inaccuracy (see other thread). The original Duracel AAs were still installed. The new software indicated “Batt 45%”, but when I removed & measured them, they both showed 1.208v, very low for alkaline batteries (nominal 1.5v-1.6v).
I replaced them with Eneloop NiMh batteries (1.38v each), and the meter is working again, although I still have the high VDC reading as before (readout is around 2.5% to 3.5% higher than actual VDC)