Typically in the case with most aftermarket ecus (megasquirt being case in point) can take the 0-5v linear output from a wideband o2 sensor, process that data, and automatically adjust the fuel maps to deliver fuelling based on an air / fuel ratio "target" table.
So, for example, you can set this target table in the MS ecu, say for the highest load column, to an air / fuel ratio of 12.0:1, do a full throttle run, and it will automatically tune the ecu to deliver these air / fuel ratios.