It can be used as a hand-held instrument or mounted on a Jacob's staff for more precise measurement, and it is small enough to carry in a coat pocket.
Abney invented this instrument under the employment of the School of Military Engineering in Chatham, England, prior to late 1870.
[1] Elliott Brothers of London registered an "improved clinometer and spirit level combined" in December 1870 based on "the old form as originally designed by Lieutenant Abney.
Along with necessary tools such as a watch, compass, sextant and plenty of paper, the committee included "a pocket level (Abney's)" in a secondary list of "additional instruments, not necessary, but convenient."
[6][7][8] These tutorial articles remain useful today, but the primary reference for usage is the 1927 Abney Level Handbook.