This weight appears to be the largest Byzantine example known, by diameter, and being purple in hue was made from the most expensive glass. The closest to it is an example in the British Museum (1986, 0602.1), green glass, also stamped with five monograms. It, however, has a diameter of only 10.37 cm, weighs in at 314 grams, and is pudgy by comparison; a bagel rather than a digestive biscuit. The Rho-Delta-Epsilon monogram is so far unexplained.
(I am grateful to Yanni Petsopoulos for the enjoyment that has come from resolving so little!)