Has anyone experienced with GE Series1

I do not understand the meaning of "MCS" and "MCR" in the Instruction List of GE series 1
The folowing is the sample of Instruction List
.
.
0304: STR TMR 620
0305: MCS
0306: STR NOT 062
0307: AND NOT 064
0308: AND NOT 065
0309: OUT 220#
0310: STR 062
0311: AND 064
0312: AND NOT 065
0313: OUT 221#
0314: MCR
0315: STR 307
.
.

MCS is "Master Control Set", MCR is "Master Control Reset". These instructions allow you to enable or disable sections of a ladder logic program. The Automation Direct Series 305 users manual explains and shows examples on pages 11-50 & 11-51. You can download the manual from the AD site.

Hi bmac, Thank you for your quickly advise.