How do you look up words in a book without losing your place?
Most people describe the same failure: they put the book down, unlock a phone, type, get distracted, and then spend several seconds finding the sentence again. The definition took two seconds and the interruption took thirty.
One traditional answer is to defer — underline the word or note it in the margin, and look everything up later. It preserves the reading, but in practice the deferred list rarely gets read.
The alternative is to shorten the interruption enough that it stops mattering. A camera dictionary does this by removing the typing and keeping your eyes on the page: with Booktionary you hold the phone over the word and the definition appears above it, so your place is never lost because you never looked away from the book.
Keeping a finger on the line while you look up is a low-technology version of the same idea, and it works.