Cheaper by the Dozen

If we have a base 10 number system, then where did the dozen come from? Also, somebody must have been thinking in terms of 12 when they invented the foot, which is divided into 12 inches. I read somewhere that the foot measurement was standardized by lining up 12 guys toe to heel, and dividing the combined length of their feet by 12. The division of the foot into 12 inches, may have come from the fact that the last joint on people's fingers average out to about an inch, and it may be that 12 of them averages out to the length of people's feet. Then there's the fathom, which is equal to six feet. That may have come from the fact that span of a man's outstretched arms, from finger tip to finger tip, is around six feet. When early sailors threw out a sounding line to measure the depth of the water under their ship, they might have measured it that way as they pulled it back in. Then there's the cubit, which originally was the distance between your elbow and the tip of your middle finger, and was eventually standardized at 18 inches. Noah's Ark was measured in cubits, and I seem to remember that the Egyptian pyramids were also. 

I know a funny true story about fathoms. I know it's true because I witnessed it. I was out on the Straits of Mackinac with some scuba divers, back in the 70s. We were watching this ocean going freighter a few miles away, and somebody commented that it didn't seem to be moving. Somebody else commented that it was pretty close to the Poe Reef lighthouse, where the water was quite shallow, and that it just might have run aground. Somebody turned our radio to the Coast Guard emergency channel and we listened in on the unfolding drama. Sure enough, she was hard aground. I read in the paper later that the ship was from Yugoslavia, but whoever was operating the radio spoke in English with no discernible accent. "I can't understand how this happened", he said, "According to my chart, the water here is 20 fathoms deep, and our ship only draws five fathoms fully loaded." The Coast Guard guy informed him that Great Lakes charts measure water depth in feet, not fathoms like the ocean charts do, which explained why the ship was hard aground. There was no significant damage to the hull, but they had to bring in another ship to offload their cargo, which took about a week, before they could refloat and get back underway.