Here exact following is not necessary, a clock drive is convenient rather than at all indispensable, and even circles one may get along without at the cost of a little time. Such is the usual situation with portable equatorials. One does not then need to adjust them to the pole with extreme precision, but merely well enough to insure easy following; otherwise one is hardly better off than with an alt-azimuth. In a totally different class falls the instrument with which one undertakes regular micrometric work, or enters upon an extended spectroscopic program or the use of precise photometric apparatus, to say nothing of photography. In such cases a permanent mount is almost imperative, the adjustments must be made with all the exactitude practicable, one finds great need of circles, and the lack of a clock drive is a serious handicap or worse. Moreover in this latter case one usually has, and needs, some sort of timepiece regulated to sidereal time, without which a right ascension circle is of very little use. In broad terms, then, one has to deal, first; with a telescope on a portable mount, with or without position circles, generally lacking both sidereal clock and driving clock, and located where convenience dictates; second, with a telescope on a fixed mount in a permanent location, commonly with circles and clock, and with some sort of permanent housing. Let us suppose then that one is equipped with a 5 inch instrument like Fig. 168, having either the tripod mount, or the fixed pillar mount shown alongside it; how shall it be set up, and, if on the fixed mount, how sheltered? In getting an equatorial into action the fundamental thing is to place the optical axis of the telescope exactly parallel to the polar axis of the mount and to point the latter as nearly as possible at the celestial pole. The conventional adjustments of an equatorial telescope are as follows: 1. Adjust polar axis to altitude of pole. 2. Adjust index of declination circle. 3. Adjust polar axis to the meridian. 4. Adjust optical axis perpendicular to declination axis. 5. Adjust declination axis perpendicular to polar axis. 6. Adjust index of right ascension circle, and 7. Adjust optical axis of finder parallel to that of telescope. Now let us take the simplest and commonest case, the adjustment of a portable equatorial on a tripod mount, when the instrument has a finder but neither circles nor driving clock. Adjustments 2 and 6 automatically drop out of sight, 5 vanishes for lack of any means to make the adjustment, and on a mount made with high precision, like the one before us, 4 is negligible for any purpose to which our instrument is applicable. Adjustments 1, 3 and 7 are left and these should be performed in the order 7, 1, 3, for sake of simplicity. To begin with the finder has cross-wires in the focus of its eyepiece, and the next step is to provide the telescope itself with similar cross-wires.