Daily Record, 1 January 1791-9 April 1794

New York Public Library: Archives and Manuscripts, Thomas Jefferson Account Book, 1791-1803.

8 pp., at the end of a book of financial accounts and miscellaneous notations.

Printed in Memorandum Books, 2:841-60.

Intermittent column headings for thermometer, Deluc hygrometer, and Saussure hygrometer.

At 15 January 1791, Jefferson began using a plus sign (+) in place of a numerical value for some readings in his column for the Saussure hygrometer, with a note: “+ this mark denotes tt [i.e. that] the humidity was beyond the highest limit of Saussure’s hygrometer.” He used the plus sign in this way until 6 July 1793.