On either side of the arm 57 are {HEAD ~ switches} 58 and 59 that are engaged by the arm 57 when the telescope 55 is swung through as small an arc as a fraction of {TAIL ~ a degree} 
On either side of the arm 57 are { HEAD ~ switches } 58 and 59 that are engaged by the arm 57 when the telescope 55 is swung through as small an arc as a fraction of { TAIL ~ a degree }
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL