What does Mappin and Webb Silver Plate with R190 markings?

To measure a horizontal angle by reiteration method?

This method is used if there are more than one angles to be measure from a certain station point. Consider the following fiqure, we will measure angles AOB and BOC using this method.ProcedureSetup the theodolite at station O, bisect the point A with a certain circle reading with face left.Rotate the instrument in clockwise direction and bisect B, note the circle reading.Then rotate and the telescope till it bisect the point C, note this circle reading also. All these reading will book into face left position.Transit the telescope and rotate the instrument through 180°, this time bisect the point C firstly and then rotate telescope in anti clockwise direction towards B and then ultimately towards A. Put these readings in face right position.You can do more than one sets of measurements for the accurate results, i have done one set and booking method is as follows,Inst. StationStn. SightedFaceCircle reading(° ′ ″)Mean of faces(′ ″)Angle value(° ′ ″)OAL10 20 5020 60AOB37 10 05 R190 20 07BL47 30 1030 11R227 30 12BOC41 10 14CL88 40 2040 25R268 40 30