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Working with the Renard series of preferred numbers specified in ISO 3.

Project description

The Renard series are a system of preferred numbers used in engineering applications which specify a geometric sequence of numbers over the range one to ten. The numbers are selected to be convenient to use and to minimise the maximum relative error when an arbitrary number is replaced by the nearest Renard number. The series were proposed by the French army engineer Colonel Charles Renard and subsequently standardised in ISO 3-1973.

For example, the R5 series contains six values (1.0, 1.6, 2.5, 4.0, 6.3) which cover a single order-of-magnitude range of values (one decade) from one to ten. These base values repeat again to cover the next decade from 10 to 100, as 10, 16, 25, 40, and 63.

This renard library is useful for selecting values from the least rounded R5, R10, R20, R40 and R80 decades, the medium rounded RR10, RR20 and RR40 decades, and the most rounded RRR5, RRR10 and RRR20 decades.



The renard package is available on the Python Package Index (PyPI):

The package supports Python 3 only. To install:

$ pip install renard

Python Interface

For full help:

>>> import renard
>>> help(renard)

In the meantime, here are some highlights.

To find the nearest R20 value to 319 use:

>>> from renard import find_nearest, R20
>>> find_nearest(R20, 319)

To find the next value greater-than or equal-to 182 in the R80 series use:

>>> from renard import find_greater_than_or_equal, R80
>>> find_greater_than_or_equal(R80, 182)

To find a few values around the specified value, use:

>>> from renard import find_nearest_few, R20
>>> find_nearest_few(R20, 5000)
(4500.0, 5000.0, 5600.0)

Command-Line Interface

There’s also a handy command-line interface. Run renard --help to see a list of commands:

$ renard --help

Usage: renard [options] <command> [<args> ...]

  -h --help     Show this screen.
  -v --verbose  Use verbose logging

Available commands:

See 'renard help <command>' for help on specific commands.

To find a nearby value, use:

$ renard nearest R20 37726

If you prefer an SI exponent symbol, supply --symbol or -s:

$ renard nearest R20 37726 -s
35.5 k

To show values around the given value, use the nearby command:

$ renard nearby R40 52e6 -s
50 M
53 M
56 M

To show the smallest value greater than or equal to the given value, use the ge command:

$ renard ge R40 52e3 -s
53 k

To show all values in an inclusive range, use the range command:

$ renard range R5 74e-9 34e-6 -s
100 n
160 n
250 n
400 n
630 n
1 µ
1.6 µ
2.5 µ
4 µ
6.3 µ
10 µ
16 µ
25 µ

To use the most-rounded Renard R”20 series (for syntactic reasons, R’20 is called RR20 and R” is called RRR20 on the command line):

$ renard range RRR20 10000 20000

To determine the multiple to which the base values of a series have been rounded, use the precision command:

$ renard precision R5

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