The eStim pod has a feature to change the output power impedance.
This feature is not present on the 4 built-in channels. eStim outputs
are voltage limited-current sources. The normal output impedance is set
for 1000 ohms. In the eStim pods there is a jumper to select a 470 ohm
impedance instead, I consider this the “high” setting, about twice the
signal current is available. There is also a third option of zero
resistance, for those situations where you want to use an external
resistor, for example a variable one.