Objective:

To find cubes and cube roots using the K scale.

General:

• The K scale is a triple-decade logarithmic scale.
• The first decade runs from 1 to 10, the second from 10 to 100 and the third from 100 to 1000. (Sometimes all indices are marked as 1.)
• The K scale is found on the body of the slide rule.
• The K scale works in conjunction with the D scale.
• Mathematically, the reason for having three decades is the fact that:

Method for finding Cubes:

• Move the cursor to the value to be cubed on the D scale.
• Read the result from the K scale.

 

Method for finding Cube Roots:

• Move the cursor to the value on the K scale.
• Read the result from the D scale.

 

Example 1:  Find the value of 1.55³.

• Move the cursor to D1.55
• Read the result K3.72

 

Example 2:  Find the value of 3.24³.

• Move the cursor to D3.24
• Read the result K34

 

 

Example 3:  Find the value of 6.45³.

• Move the cursor to D6.45
• Read the result K268

 

Example 4:  Find ³√4.5.

• Move the cursor to K4.5 (first decade)
• Read the result D1.65

 

Example 5:  Find ³√36.5.

• Move the cursor to K36.5 (second decade)
• Read the result D3.32

 

Example 6:  Find ³√275.

• Move the cursor to K275 (third decade)
• Read the result D6.5

 

Practice Questions:  Evaluate the following.

1. 1.94³ (Ans: 7.3)
2. 3.53³ (Ans: 43.6)
3. 7.84³ (Ans: 482)
4. ³√5.7 (Ans: 1.79)
5. ³√45 (Ans: 3.56)
6. ³√380 (Ans: 7.24)