For me, my meals are roughly divided from very low carb to very high carb, and I dose based on that instead of exact carb count. I do check all packages and lots of unlabeled fresh food though, so I'm very aware of if I choose highish or lowish carb food. Very little maths involved.
A big improvement for me was when I found out I need way more insulin for the same carbs in the morning than I do in the evening.
What also helped was changing my diary from the way you note it to using grid paper with the hours of the day on the top row and using the columns to note glucose level, insulin dose, exercise, and food (I simply wrote roughly what foods I had, not the carbs, which would be even neater). This enabled me to see correlations in the blink of an eye instead of looking back and forth and having to guess at what time I did what.
I live in Friesland, way up north and close to he Waddenzee
. Where does your friend live?