I have a character. One of their parents died. Said parent was cremated, and then - by their own choice; this is a quasi-religious thing - their cremains were mixed into tattoo ink, and the character was tattooed with that ink.
The character in question is a paramedic for a religious order, as was their parent before them; before said parent's death, they both agreed that said cremain tattoos would be in the form of writing - specifically writing on various types of first aid, as a memory aid - not for simple stuff like CPR, stuff like "here's how you identify and treat a sucking chest wound", or "here's how you insert a stent".
With modern tattoo technology, how small can words written with cremain ink be? This is relevant, since the character in question is trying to pack as much information into as little of a space as possible.