I’m looking for rowing machines, and I’m wondering which kinds have adjustable resistance without using electricity. Can you help me figure this out?

From a very lazy google session, it looks like flywheel is my cheapest option. I also can’t tell whether the magnetic types require electricity (it seems like they would, but maybe they are human-powered somehow?).

- I don’t care whether the console and stuff work without electricity. I just need the core machine itself (and the resistance) to work without electricity.
– When I say “adjustable resistance,” I mean a setting that I can change, not just resistance that changes in response to how hard I’m rowing.
– The best way to find this out is to look at the product documentation. HOWEVER I am looking for advice to help me with my online search for a used rower that will work. I’ll be going through a lot of listings and it likely won’t be practical for me to look up the specs for every single one.