The gentleman and traders guide containing a description and use of the newest invented instrument, ever made publick, for preventing frauds by counterfeit gold ... the instrument is neatly made in brass, and very easily portable for the pocket - Bradford, William (Printed by S. Creswell, 1770)
By W. Bradford, R. Darby and J. Hulls, according to Goldsmiths' Library. - Dated about 1770 by Goldsmiths' Library. - Goldsmiths'-Kress no. 10662. - OCLC, 24601307. - Reproduction of original from Goldsmiths' Library, University of London