moneyers' weight

1

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 19^th century at the latest these units had been entirely replaced by decimal fractions of the grain.

It is difficult to see how the smaller units in the sequence could have been measured in the 17^th century, or before. 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.

					pennyweight
				grain	24
			mite	20	480
	droit or droict		24	480	11,520
	periot	20	480	9,600	230,400
blanck, blank or blanc	24	480	11,520	230,400	5,529,600

sources

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.

2

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

					denier
				grain	24
			prime	24	576
		second	24	576	13,824
	third	24	576	13,824	331,776
fourth	24	576	13,824	331,776	7,962,624

Sources

Moryson's page is too complex to reproduce here. A PDF image of the chart, as set for the 1907 edition, is here.

Fynes Moryson.
An Itinerary containing his ten yeeres travell through the twelve dominions of Germany, Bohmerland, Sweitzerland, Netherland, Denmarke, Poland, Italy, Turky, France, England, Scotland & Ireland.
Glasgow: James MacLehose and Sons, 1907.
Part I, Book III, Chapter 6.
Page 136 of this edition. The first edition was published in 1617, but the travels took place between 1591 and 1603.

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.

Act anent the mint

there shall be a standart or printed table keeped in the mint house of the value of money or bullion, according to the denominationes of weights used in the mint of deniers, graines, prymes and seconds, and the ordinary denominations of pounds, ounces, drops and graines by which merchants or others may know what they are to give in or gett out when there bullion doeth arrise above or fall below the standart appoynted. ...

the sexty shillings Scots pieces is to weigh, according to the denomination of weights used in the mint, tuenty-one deniers, eighteen graines, ten prymes, eightein seconds, and [in] the ordinary denomination of weights, fourtein drope, eightein graines...

James VII. Parliamentary Register. At Edinburgh 14 June 1686.