Kath and I have the same kind of calculators, purchased years ago, when we weren’t even working together. It has waterproof buttons, a solar panel and when she uses hers, it always gives the right answers.  Mine’s a bit chipped, has fallen off barrels, been soaked with wine, water and sweat (eeewwhhh) and a few tears.  I don’t trust it anymore, cause it’s made so many mistakes!  But I 100% trust Kath and her calculator to get the right answers and look after everything that makes the business run properly. Thanks Kath.