Instruments have been invented by Alvan Clark and Sir Howard Grubb for measuring with the spider-line micrometer angles which are larger than the field of view of the eyepiece.
Alvan Fisher >>
C. Ord (1867), Alvan C. Gillem (1868) and Irvin McDowell (June-July 1868), and by Gillem (1868-1869) and Adelbert Ames (1869-1870).
Diameter by Alvan Clark & Son of Cambridge, U.S.A., and with a mounting, dome and rising floor by Warner & Swasey of Cleveland, Ohio, U.S.A. The reader will gather a good general idea of the design from fig.
Among the inheritors of his renown were Alvan Clark and Alvan G.