A few questions about Karma

[revolver]

Each time libs/Karma.php is run does it calculate each user's Karma for the given time period ($history_from) and then merge that with the user's previous karma rating?

Is there a reason why 6 and 20 were chosen for the minimum and maximum Karma values? Is it safe to change these?

If we are running Karma as a cron job should we be setting $history_from in libs/karma.php to the same frequency that we are running the cron job?