The leveling off would occur at about 3,000 feet and somewhere between the estimations and the slide rule I came out dead on. The flaps started to extend and the engines increased in power as the sweep second hand on my wristwatch which Mom had used as a WAC Sargent in WW2 ticked past the last 5 seconds of my prediction. ]]>

« …slide rule does NOT tel you where to put the decimal point. »

A quite simple method exists !

For a multiplication, using the slide rule’s right side, the number of digits of the product is equal to the sum of the number of digits of the factors.

8 400 x 12.5 gives a number of digits of the product of 4 + 2 = 6 digits, reading the slide rule, the answer is 105 000.

For a multiplication, using the slide rule’s left side, the number of digits of the product is equal to the sum of the number of digits of the factors minus one digit.

12.5 x 0.45 give a number of digits of the product of 2 + 0 – 1 = 1 digit, reading the slide rule, the answer is 5.625.

For a division, using the slide rule’s right side, the number of digits of the quotient is equal to the difference between the number of digits of the dividend and the divisor.

2600 / 0.0042 gives a number of digits of the quotient of 4 – (-2) = 6 digits, reading the slide rule, the answer is around 619000.

For a division, using the slide rule’s left side, the number of digits of the quotient is equal to the difference between the number of digits of the dividend and the divisor plus one digit.

625 / 2.4 gives a number of digits of the quotient of 3 – 1 + 1 = 3 digits, reading the slide rule, the answer is around 260. ]]>

With a slide rule, you can’t mistake precision for accuracy – two very different things!

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