To demonstrate the use of the Deci-Point's scales, we first look at a simple example in six steps. Of course these steps are only being used for clarity of the solution.
63500 x 0.00155
Step 1:
Using the front of the slide rule (like any other slide rule), we calculate the significant figures of the product 635 x 155 arriving at the digits 984.
Step 2:
On the back of the slider, perform the same calculation using the condensed C and D scales (C' and D') on the left. We find that the result falls in region 0 (zero) for multiplication.
Note that these calculations do not have to be accurate but you should take some care with them. However, we are only interested in the region that the answer will fall. Fast and furious? ... Maybe!
Step 3:
Align the inverted triangle above the 0 (zero) on the RN-DZ scale.
Step 4:
Now we determine the requirements for the difference number (DN).
- Count the number of factors, F. In this case 2, i.e. from 63500 x 0.00155.
- The number of zeros, Z. In this case 2, i.e. from 0.00155.
- The number of digits, D. In this case 5, i.e. from 63500.
Step 5:
Calculate the difference number (DN)†.
DN = D - (F + Z) = 5 - (2 + 2) = +1
Step 6:
Below +1 on the DN scale, we locate +2 on the RN-DZ scale. Note that the slider has not been moved since the inverted arrow was aligned with 0 (zero) on the RN-DZ scale, step 3.
This value means that the result has 2 (two) digits in front of the decimal point. Hence 98.4 is the answer to our calculation.
† Technically, the difference number (DN) is really the term used when the denominator is not equal to 1.
Proceed to Division Example
