Mr Lo, or ehm Huang, which ever it is you are.

The tool is indeed an Inclinometer. This one caught my eye since it was less resembling of just an improved level which many of the other makers derived their products in design. The inclinometer, also helped lead to other developments with builder’s levels and transits.

This tool was made by the Patent Level Company.

"The Patent Level Company - was located in Bridgeport, Connecticut according to the stamp on the base of the level. To date, however, no other record of the existence of this company has been found. The patent date - May 8, 1866 - corresponds to the date on which a patent was granted to Andrew. J. Vandergrift of Cincinnati, OH, for an "Improvement in Spirit Levels." "