Free RAM memory from free command and Mobaxterm

I have several servers running Debian 10 or 11. I use Mobaxterm (Link ) for SSH into the servers to check the status of the services and the RAM usage. I notice that the > free --mega -t shows a amount of free RAM that differs from the one provided by the Mobaxterm (used RAM/total RAM in the red rectangle) in the bar on the bottom of the SSH windows. This is the situation: Why Mobaxterm shows 0.64 Gb of RAM are used and the "free" shows 170 Mb are used? Which is the best way to check the used and the free RAM? Why there is this difference between the two methods? Thank you for the help!