On October 22 I presented the 'Slide Rules Rule' lesson at the Math Teachers' Circle at San Joaquin Math Teachers' Circle. This is a lesson I've been developing over the last several years and I really enjoyed the opportunity to share it with the SJMTC. They added to the lesson by sharing the time and math with me and then going over the mathematical practices and pedagogical methods I used at the end. That was a really cool experience. They highlighted my addition of "wishful thinking" to their problem solving approaches list and talked about how I had started slow and kept the whole entire group moving forward during the lesson.

Basic gist... we start by putting the amazingness of the slide rule in context - we had an airplane and sent people to the moon prior to electronic computing like we think of it today. Instead we used slide rules, charts, and less significant digits (that's were good error estimation is important!)

From there we talk about the addition and multiplication tables and compare the properties of the addition table that are nice and we wish were in the multiplication table. Specifically the addition table has these beautiful lines of 1 number so you can travel along that line and see directly what number added to x equals that number. We wish we had this linear property in the multiplication table. We rescale the multiplication to make this happen and surprise - we get the exponential scale that's used to make slide rules.

Yay!

From there we spend the rest of the day playing with slide rules! It's great fun.