I swim a mile three days a week, one problem given how repetitive it is I would lose count. In my case 36 (up and back 25 yard pool) laps are just over a mile. Almost all pools have Pace clocks (see picture) with any type of swim team, this is for those of us who train but are not on a swim team.
I have a counter I use that keeps track of laps and pace but it has too much glare to be any good beyond looking at my pace per lap when I am done. Being an engineer I unconsciously solved my problem. I extrapolated my single case solution to accommodate any one who swims distance in a pool.
Pace clock on the wall.
Step 1: Reasoning
As I got lazy in my swimming thinking about anything but my stroke, I found my time never got any better ranging from 33:40 – 34:15. Determined to get better I started looking at the pace clock just after the flip, I did some quick math in my head to determine that to swim a sub 33:00 mile (36 laps in my pool is greater than a mile by 120ft) I needed to swim an average of 55 seconds per lap. With that in mind each lap I tried to make sure the sweep hand on the clock appeared to move 5 seconds backwards with each lap to get the 55 second pace.
I further extrapolated that if I counted how many times the sweep hand passed the zero I could determine if I was on schedule. A good rule of thumb was to be gaining (for lack of a better term) about 1 minute every 10 minutes. That by 20 minutes I should be 2 and 30 to be close to 3.
Step 2: Example
I could not paste the table so I took a screen shot the col are a little off but you should be able to get it. here is an example.
For example if your goal is 33min/Mile:
Mile time, Pace, clock back/lap, clock back10min, 20min, 25min, 30min @mile mark
33:00, 55, 5, 00:50, 01:40, 02:05, 02:30, 03:00
You need to remember 3 things: start time (so you can go for a set time before checking and know when you are done), your goal pace at -5 seconds per lap, and keep track each time the sweep (second) hand passes 60/0 to count minutes. Given you will only vary a second or two per lap (at least you should if you try to keep pace, I start strong but by the third lap my pace does not vary much) the total time is not much of an issue.
I know if I go 3 minutes back in 33 minutes total I know I swam a mile and know my pace.
Now if the clock went back only 2:30 at 33min I know I should swim another lap to make it a mile, in any case until you know your “time zone” you swim keep going to the next 5 minute mark to make sure you get your mile as a penalty for not making your time. Soon you will find by keeping an eye on your pace you will improve to either reach your goal or find your current limit.