Write a short note on: Preferred series and numbers.

Preferred series and numbers:

Preferred numbers are used to specify "sizes" of product.

Preferred numbers are the conventionally rounded off values derived from geometric series, including the integral power of 10 and having common ratios the following factors:

                                                              ⁵√10, ¹⁰√10, ²⁰√10, ⁴⁰√10, ⁸⁰√10

These ratios Ø , knows as step ratios, are approximately equal to 1.58, 1.26, 1.12, 1.06, 1.03 respectively.

The system based on use of geometric progression to develop set of numbers. There five basic series denoted as R5, R10, R20, R40, R80 series, which increases in steps of 58%, 26%, 12%, 6%, 3% respectively. 

The series are as follows:

R5 Series                                      ⁵√10=1.58

R10 Series                                  ¹⁰√10=1.26

R20 Series                                  ²⁰√10=1.12

R40 Series                                  ⁴⁰√10=1.06

R80 Series                                  ⁸⁰√10=1.03

Series is formed by taking first number and multiplying it by a series factor to get second number.The second number is again multiplied y series factor to get third number.It continues until complete series is formed up.