@gillian – I too carried a calculator around when I was first diagnosed – I just can’t do sums! (My A levels were in English Lit, Geography and History and my degree is law – I do writing, not maths!) I now use my mobile for calculations.
When I started carb counting I carried around a little notepad and every time I had a meal I wrote it down and the amount I injected for it. So, for example, “Spaghetti bolognese = 9 units”. Next time I had spag.bol I would just look it up in my notebook and inject accordingly (obviously allowing a bit either way if BG was high or low; or adding / subtracting if portions were abnormally large or small). Before long I had a useful cheat-sheet of meals and the amounts I needed to stick in.