Last week we noticed quite a few small sand dollars — or perhaps they should be called sand quarters or sand dimes? — washed up on Salmon Creek Beach.
So this was intriguing. Eric and I guessed that the sand dollars we saw ranged in size from smaller than a dime, to as large as a quarter, with the average size being about dime-sized. The true range we measured was 10 to 23 mm in diameter, with an average size of about 17 mm.
How well did they match the measurements of the coins? I had never measured the coins before, but tonight I measured them — a quarter is 23 mm across and a dime is 17 mm across. Amazing! Our estimates were pretty darn good relative to the coins! But we've both measured a lot of things for many years, and used a lot of coins, too, so I guess that shows you the value of practice and repetition (...or we just got lucky).
I wrote about sand dollar skeletons a few years ago, so if you'd like to learn more about them, you can review the post called "Petals and grooves".