Tip calculator/card

[smackababy]

Holy shit. My mom is 80 and doesn't know how to tip. At this, point .... I want her to have a damned card or calculator or something. If math were the issue, I wouldn't be posting here.

How does one "not know how to tip". You can tell her "Mom, tip 10% no matter what" and be done with it. No card needed. Unless, you are trying to say she doesn't have the capacity to understand and remember that sentence.