moneyers' weight

In England, a sequence of units supposedly used for medicine and precious metals, produced by subdividing the grain alternately by 20 and 24 (continuing the pattern in troy weight). By the middle of the 19th century at the latest these units had been entirely replaced by decimal fractions of the grain.

The smaller units in the sequence must have been purely conceptual. Although the system is described in several old documents, it looks like the creation of some monk's overwrought imagination. Today, a sophisticated $10,000 laboratory analytical balance weighs with an accuracy of roughly ± 5 micrograms. The blank would have been about 0.28 micrograms.

				grain
			mite	20
		droict	24	480
	periot	20	480	9,600
blank or blanc	24	480	11,520	230,400

Scotland had a similar scheme of subdivisions, except instead of alternating 20 and 24, every division was by 24. See source 1 below.

Sources

the Troy weight onely is used, containing twelve ounces, every ounce twenty penie weight, every penie weight twentie and foure grains, and every grain twenty mites, every mite twenty and foure droicts, everie droict twentie periods, everie period twentie and foure blanks, although superfluous (but in the division of the subtile assay) which in Scotland are all divided by twentie and foure, from the denier wherof they reckon twentie and foure to the pound Troy, so twentie and foure graines, Primes, Seconds, Thirds and Fourths all by twentie and foure.

Gerard Malynes.
Vel Lex Mercatoria, or the Ancient Law-Merchant.…
London: Printed by Adam Islip, 1622.
Page 292.

Besides the common Divisions of Troy Weight, I find in Angliae Notitia, or, The Present State of England, Printed in the Year 1699, that the Moneyers (as that Author calls them) do Subdivide the Grain
Thus
    24 Blanks = 1 Periot.
    20 Periots = 1 Droite.
    24 Droites = 1 Mite.
    20 Mites = 1 Grain, &c. as before.

John Ward.
The Young Mathematician's Guide. Fourth Edition.
London: Printed for A. Batterworth and F. Fayrham, 1724.
Page 32.