The "Instrument Selector" is essentially a new fold mirror that has been installed in the acquisition boxes of both SpUpNIC and HiPPO<ref>''22 Feb 2024: the implementation of the fold mirror in HiPPo's acquisition box has not been completed at time of writing</ref> that allows the observer to switch between two instruments: a "primary" and a "secondary" instrument where the primary instrument is either SpUpNIC or HiPPo and the secondary instrument is always a new SHOC system. In other words, a SHOC is from now on permanently available on the 74-inch.
Figure 1 ('''still need to add figure'''''Italic text'') shows the new SHOC system mounted to the side of SpUpNIC's acquisition box. The new SHOC system replaces the old guider box that use to migrate between SpUpNIC and HiPPo. The new SHOC system is incorporated into a newly designed off-axis "pick-off" style guider system that can accommodate a filter wheel unit and SHOC camera behind the guider. The new SHOC system also has a focal reducer built in providing just over double the FoV-width compared to the the old system (2.7' × 2.7' for the new system vs. 1.3' × 1.3' for the old setup).
To select between the primary instrument and SHOC, a user can actuate the fold mirror in/out of the beam to direct the science beam towards the desired instrument (see Figure 2 below that indicates the button on TCS that actuates the fold mirror). When the fold mirror is IN beam and the guider's XY stages are "centred" then the guider camera also functions as a "target acquisition" camera for SpUpNIC/HiPPo, similar to the old system. Also as in the old system, the guider can patrol the area of the large annulas mirror to acquire an appropriate guide star.