He uses a pencil, paper and a mechanical calculator to tally up the bill, which I absolutely understand when your career is in IT.

When the alternative is either having to search, evaluate, compare, select and configure an application for that purpose that you’re never quite happy with, or to scope, design, develop, test, deploy, maintain, eternally find things you wish you’d done better, refactor, realise you’re spending your free time on doing more of your job, regret your life choices, resolve to only make this last improvement and then call it good enough, renege on that promise to yourself a week later, burn out, curse that damn app for ruining your hobby…

…yeah, using the most trivial low-tech solution possible does look rather sensible.