Erl shared his voltage reference project in the forum:
I had almost 6 x 6 cm left over on a 10 x 10 board I was ordering from Seeed Studios, so inspired by the Mr. Ref voltage reference project, I made something similar.
It’s based on the MAX6126 2.048 V reference, uses 3 AAA batteries for power, and fits in the Dangerous Prototypes Sick of Beige 60 x 60 mm case.