Blogging the log tables

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I grew up in the Imperial Valley, the southeast corner of California. Big farming area in a desert.

My dad worked for the Imperial Irrigation District as a zanjero, a ditch rider. Farmers and other water-users like cities and industries buy water, which is delivered through a series of canals, originating in the Colorado River 70 to 100 miles away. They have done this for about 100 years.

They measure water to sell by the acre-foot which is an acre covered a foot deep in water. (For metric people, an acre is about 40 meters by 100 meters and a foot is about 30 centimeters, so: 1.2 million liters.)

But the way it was measured was to find out how deep the water was at the delivery gate it flowed through and how big the gate was.

It works out to a gate a foot wide and a foot tall with a foot of water above the top of the gate; if the water runs for 24 hours, it comes out to almost exactly an acre-foot, only off by ~1/2 %.

Dad was responsible for making sure that the water ordered was delivered. Zanjeros work at the delivery end, hydrographers measure the water at the supply end, but both jobs involve calculating water flow through a complex system.

They had tables for figuring this all out based on different-sized gates and different heads (depths) of water and how long it ran.

I found this out when I was in junior high, learning logarithms and calculus. But my dad did all the math in his head. Saved him an hour or two a day looking things up and doing the math on paper.

He had memorized the log tables in the back of the books. Dad said it wasn't that hard; you only needed the first two digits, and you could guess the third. And he only had to be right to about 2% error.

I showed him my slide rule and he said that would have been handy to have.

Now, we have powerful computers in our pockets.

No one in the rest of human history is going to have a good reason to memorize the log tables.

Enjoy the future today.

Hugs,
Erin

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