Objective:

To divide two values using the C and D scales.

General:

• The two most basic and necessary scales to work with are the C and D scales. 
• The C and D are identical scales and are single-decade logarithmic scales.
• When dividing two values, we make use of one of the law of logarithms, which states that the logarithm of a quotient is equal to the difference of the logarithms of the factors.  Mathematically, we write this as:
  
• The left or right index of the C scale may be used.  The right index is used if the left index goes off scale, i.e. goes too far outside the body of the slide rule.

Method:

• Align the numerator on D with the denominator on C.
• Move the cursor to the left (or right) index on C.
• Read the result on D.

Example 1: 550 ÷ 32

• Align C32 over D440
• Move the cursor to C1
• Read the result D17.2

 

Example 2: 455 ÷ 7.6

• Align C7.6 over D455
• Move the cursor to C10
• Read the result D59.9

 

Practice Questions:  Calculate the following quotients.

1. 87.5 ÷ 37.7 (Ans: 2.32)
2. 1029 ÷ 9.7 (Ans: 106.1)
3. 3.14 ÷ 2.72 (Ans:1.15)
4. 0.0059 ÷ 1.98 (Ans: 0.00298)
5. 10.5 ÷ 30.3 (Ans: 0.347)