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si units

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International System of Units (SI Units) or MKS units for seven base quantities of measurements and their derived quantities are unified. Specific symbols are designated for all. Only symbols can be used or written in full spells for these units of measurement, for example, there are 30 s or 30 seconds in half a minute. Not 30 sec.

Note 1: Units are always written and read as singular. We can not write 30 seconds, yes it is 30 seconds.

Note 2: Always give one space after numbers and symbols. Example 35 s is correct. 35s is not correct.

Let us quickly see how to present the symbols of various units:

1. Time: symbol (s). Read as a second. It is small s . Writing 10 s and 10 Second is correct. Use of 10 Sec. or 10 SEC. Or 10 seconds is not correct.

2. Mass: symbol (kg). Read as Kilo Gram. It is small k and small g. Writing 25 kg or 25 Kilo Gram is correct. The use of 10 KG or10 KGM or 10 KGS is not correct.

3. Length: symbol (m). It is small m. Writing 20 m or 20 Metres is correct. Note the spellings Metre is for measurement of length and meter is used for some indicating devices. Writing 20 Mtrs. or 20 Mt. or MTRs is not correct.

4. Temperature: symbol (K). Read as Kelvin. It is capital K. Kelvin is a base unit. Temperature’s popular conventional units for daily use are Degree Celsius and Degree Fahrenheit. Writing a temperature of 340 K or 240 Kelvin is correct. 240 °C and 240 °F (small symbol of degree ‘°’ appeared before C and F but not a symbol of degree is used when presented the temperature in Kelvin).

Note: 240 K and 240 °C and 240 °F are not the same values. There are certain conversion formulae for finding equivalent temperatures given on one scale to the others.

5. Current: symbol (A). Read as Ampere. It is capital A. Ampere is used for both alternate and direct current measurements. Writing 10 A or 10 Ampere is correct. 10 Amp. and 10 Amps. is not correct.

6. Volt: symbol (V). Read as Volt. It is capital V. 220 V or 220 Volt is correct.

220 Vol. or 220 v is not correct.

Note: While noting down the measurement data, the type Alternate Current (symbol: ac) and Direct Current (symbol: dc) are used for clarifications. For example, 12 Vdc and 220 Vac are correct. 12VDC and 220VAC and 12vdc and 220vdc etc. are not correct.

7. Electrical Power: symbol (W). Read as Watt. It is capital W. Writing 100 W and 100 Watt is correct. 50 w or 50 Wt. or 50 Watts is not correct.

8. Volume: symbol (L). Read as Litre. It is capital L. Writing 10 L and 10 Litre is correct. 10 l or 10 lt. or 10 Litres or 10 ltr or 10 10 lit are incorrect forms.

Note: there are other base and derived units which need clarifications about their symbols and these will be shared shortly in some other article.

How to write numbers in the SI system of units? The followings are the rules and examples are provided for registering the numbers for science, engineering, technology-related measurements. This set of rules does not apply to financial data.

Rule 1: On the left side of the decimal point after every three digits give one space. If there is no decimal then after every three digits from left to right give on space and repeat till the complete data is written.

Rule 2: To the right side of the decimal point after every three digits give one space and repeat a space after every three digits till the data is complete.

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Examples:

3714518730897.618530832 is not correct

3 714 518 730 897.618 530 832 is correct

55231647 not correct

555 231 647 correct

0. 54611 not correct

0.546 11 correct

1598.5409 is not correct

1 598.540 9 is correct

3745.10 is not correct

3 745.10 is correct

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