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Decimal Round-Off



Bullet designs that have linear measurement decimal values ending in digits that do not end in either .000 or .005 are generally awkward to comprehend and difficult to work with. Using the assumption that 0.0025" of linear difference is of small significance in cast bullet design, rounding the linear dimensions to the nearest 0.000" or 0.005" produces a clean, comprehensible design.

A decimal number may be rounded off to the nearest 0.005 by either of two methods. Inspection or by using simple arithmetic. After understanding the arithmetical method, the inspection method is easy to use.

Using an arithmetical approach produces precise results.

To round a decimal number off to the nearest 0.005, so that the last number is either a " 0 " or a " 5 "multiply the number by 2000 then round it off to the nearest whole number and divide by 2000.

A decimal number that requires rounding to the nearest 0.005 is composed of two parts - a whole number and a decimal number. Such as those below.

The whole number, on the left, can be either a zero or a number larger than zero.
The decimal number on the right may also be a zero or a number larger than zero.

Step #1    1.1111,   0.5654356,   1.003576,   0.758,  0.999

     Start by multiplying the number in Step #1 by 200

Step #2     222.22,   113.08712,   200.7152,    151.6,   199.8

     Round the number in Step #2 off to the nearest whole number using the following process:
     If the number on the right of the decimal is less than  .5  write the number on the left of the decimal as a whole number.
     If the number on the right of the decimal is equal to or more than  .5  then add 1 to the number on the left of the decimal and write it as a whole number.

Step #3     222,   113,     200+1 = 201,     151+1 = 152,    199+1 = 200

     Divide the number in Step 3 by 200

Step #4  222 / 200 = 1.110,  113 / 200 = 0.565,  201 / 200 = 1.005,  152 / 200 = 0.760,  200 / 200 = 1.000

     Each number is now rounded off to the nearest 0.005

     1.1111    0.5654356   1.003576    0.758      0.999
     1.110      0.565          1.005         0.760      1.000

To round a decimal number off to the nearest 0.010, multiply the number by 100, round it off to the nearest whole number and then divide by 100.

To round a decimal number off to the nearest 0.001, multiply the number by 1,000, round it off to the nearest whole number and then divide by 1,000.

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