Clear Technical Writing
Special Topics

Numbers and Units

In non-technical writing, we often use full words for numbers.

We arrived three-quarters of an hour ago and found seven swans swimming on the pond. Twelve days from now there will be about eighty.

We express numbers in digits almost all the time in technical writing.

For your writing to be clear, you must be consistent with your use of numbers and units of measurement.

Be consistent with conventions

Use digits when using the symbols % or $, and attach the symbol to the number.

The $5 charge was a 10% increase.

Use digits when using the abbreviations a.m. or p.m.

We attended the 10 a.m. meeting.

Use digits when identifying a date.

On April 1, pranksters write April one.

Always put a space between a number and its unit of measurement.

It weighs 50 kg.

Never indicate a plural quantity by adding an s to a unit of measurement.

[x] It weighs 50 kgs.

Use lower-case letters for units of measurement, except for letters that stand for a person's name and for letters that indicate a multiplier greater than 1000.

At 120 V, the 1.5 hp motor drew 10 A.
[Alessandro Volta, Andre Ampere]

The wind turbine produces 10 kW.
[James Watt]

My radio is tuned to 89.3 MHz.
[Heinrich Hertz]

Use the abbreviation No. for the word number in front of a number in digits.

We are No. 1 in sales for No. 2 pencils.

When a number is preceeded by a word like Box, Check, Invoice, or Room, do not use the abbreviation for number.

I included Check 835 for Invoice 2106.

Note: Using no. instead of No. is prefered in some technical communities.

Be consistent with yourself

When you create your own abbreviation or unit of measurement, define it before using it and be consistent with conventions and with yourself.

If it's heavier than 45 kg, it's designated an extra-heavy parcel (xp). The distribution warehouse ships more than 20 XPs per shift.

If it's heavier than 45 kg, it's designated an extra-heavy parcel (xp). The distribution warehouse ships more than 20 xp per shift.

Edit your writing by spotting problems with numbers and units of measurement.

We paid the $ 860 charge on January tenth at four p.m. It was a fifteen % increase over what we paid last year for a 3hp fan. Please deliver it to Room No. 2 in our laboratory.
  

Lesson: Numbers and Units
Module: Special Topics
Course: Clear Technical Writing