[3][4] At first he studied law, but became a student of Johann Georg Tralles and changed his academic focus to astronomy, mathematics and physics.

[4] In the summer of 1793, he studied under scientists Jean-Charles de Borda, Jean Baptiste Joseph Delambre, Jérôme Lalande and Antoine Lavoisier in Paris.

[7] Through the influence of Albert Gallatin, he was appointed by President Thomas Jefferson as professor of mathematics at the United States Military Academy from 1807 to 1810.

[8] Hassler was unpopular as a teacher and was dismissed on 31 December 1809, when John Calhoun, then Secretary of War, realized that Congress had not authorized the hiring of civilians to staff the academy.

[9][14][15] After Hassler's return to the United States, President James Madison appointed him the first superintendent of the Survey of the Coast in 1816.

As early as February–March 1817, Hassler standardized the bars of his device which were actually calibrated on the Committee Metre (an authentic copy of the Mètre des Archives) which was the property of the American Philosophical Society, to whom it had been presented by Hassler himself, who had received it from Tralles, a foreign member of the French Committee charged with the construction of the standard metre by comparison with the Toise of Peru, which had served as unit of length in the measurement of the meridional arcs in France and Peru.

27 allotted to the United States in 1889 at the first General Conference on Weights and Measures arrived in Washington, D.C.[16][10][17][18][19][4][20] However, Hassler had exceeded the spending limitations that had been set for his trip to Europe, and the resulting controversy foreshadowed the frictions between Hassler and the American Government that would plague his career.

They used separate weights and measures from wherever they could be obtained - most of them came from England - and in some cases the customhouses depended upon the ordinary standards of local officials.

With the approval of Secretary of the Treasury Samuel D. Ingham and President Jackson he determined to adopt standards for the United States and produce and distribute them to the customhouses.

[4][12][21] On 3 March 1831, Samuel D. Ingham reported to the President of the Senate Hassler's inspection far advanced and mentioned the Troughton scale as one of the authentic units adopted for the comparison.

By reason of the joint resolution of 1836, the Office of Weights and Measures in the Coast Survey is considered formally established as of that date.

[12][11][32][33] He also wrote a defense of his work on the coast survey and published it in the Transactions of the American Philosophical Society in 1825.