They could use a computer with a pinyin input method and see a list of characters that have that pronunciation. In this case they could enter "tì" or "ti4" and

They could use a computer with a pinyin input method and see a list of characters that have that pronunciation. In this case they could enter "tì" or "ti4" and get a list something like https://en.wiktionary.org/wiki/t%C3%AC#Romanization https://en.wiktionary.org/wiki/t%C3%AC#Romanization but probably with a nicer interface. (They do have to be able to recognize the written character when they see it. Here the character Moser was trying to produce is one of the forms under item 5.) Also, there are statistical techniques to show the most probable characters in context following particular other characters, not just the most frequent characters overall. For example, if Moser had just typed 喷 on a computer and then was looking for a character pronounced "tì", software could suggest 嚏 as the most likely possibility in that situation. But it would probably be a fairly terrible situation when not using a computer.