# I am skipping some boilerplate
package Calc;
sub new {
  my ($configfile, ...) = @_;
  my $config = read_configfile($configfile);
  my $internal_data = {
    config => $config,
    stash => {}
  };
  # bless etc.
}
sub distance {
  my ($internal_data, $params) = @_;
  # internal_data holds config,
  # $params holds from, to and anything to override
  # config just for the life of this call
  ...
  # optionally save results to the stash
  $internal_data->{stash}->{distance} = 42;
  # return something back
  return {
   errormsg => 'nothing',
   status => 1, # correct
   distance => 42
  };
}