The pendulum astrolabe with an electronic transit detector after the principle proposed by I. Tsubokawa has comparable accuracy to those of the Danjon astrolabe and P.Z.T. even in the field. After the same principle, an instrument for observatory use is being constructed, in which all observational processes are done automatically under the predetermined programs. The necessary mechanisms for automatic operation are as follows:

(1) Azimuth setting mechanism for respective stars observed.

(2) Mechanism which turn the telescope through 180° during the passage of a star near the mean altitude.

(3) Tracking mechanism in azimuth direction.

(4) Tracking mechanism in altitude direction.

(5) Read-out mechanism of the times of passages of a star on respective altitude circles.

Of these, the altitude tracking mechanism directly affects the observational accuracy. The rotation of a plane parallel glass compensates the diurnal motion of a star and keeps its image in the state of repose on the edge of a prismatic knife of the electronic detector. The rotating mechanism gives to the plane glass combined rotation of the two parts; the servo-system of the electronic detector and the system of generating the variable rotational velocity corresponding to the diurnal motion of a star. The extreme accuracy in the earth's atmosphere is expected.