According to the manual posted at this link
https://www.manualslib.com/manual/91312 ... =19#manual
it doesn't matter.
"The CMK has a number of safety features. For easy operation, an isolated +12 Volt, DC adaptor of either positive or
negative polarity may be used. It must have a 2.1mm co-axial power jack. A bridge-rectifier is present within the
CMK to ensure the proper polarity. A 500mA self-resetting Polyfuse provides over-current protection from the
common power supply."
Ray