I'm not sure if the Mercedes CC circuit has a minimum speed to set, but the resume function should work at 30 or above (I've never set it or resumed below 30) whether or not you've stopped. If you've shut the car off, the resume setting will be lost until the CC is set again.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]