A stored procedure can return several values; each must be defined as an output variable in the stored procedure and in the calling statements. You can abbreviate the output keyword to out.
exec myproc @a = @myvara out, @b = @myvarb out
If you specify output while you are executing a procedure, and the parameter is not defined using output in the stored procedure, you see an error message. It is not an error to call a procedure that includes return value specifications without requesting the return values with output. However, you do not get the return values. The stored procedure writer has control over the information users can access, and users have control over their variables.