The US Army developed some wheeled vehicles that could negotiate a 60 percent grade. A 60 percent grade rises at an angle of 27 degrees from horizontal. Two newspaper journalists encountered the information and wrote articles about the vehicles for their readers. Both journalists mistakenly wrote that the vehicles could negotiate a 60 degree slope. No wheeled vehicle to date (circa 2003) can climb a 60 degree slope. Gravity prevails!
Written communication can fail even though we attempt to communicate effectively. Sometimes we do not intend to communicate effectively. Consider the following paragraph from advertising literature for a major credit card.
Finance charge is calculated by multiplying the daily balance of each segment of your account (e.g., cash advance, purchase, special transfer, and special purchase) by the corresponding daily periodic rates(s) that has been previously disclosed to you. At the end of each day during the billing period, we apply the daily periodic rate for each segment of your account to the daily balance of each segment. Then at the end of the billing period, we add up the results of these daily calculations to arrive at your periodic finance charge for each segment. We add up the results from each segment to arrive at the total periodic finance charge for your account.
If you intend to communicate effectively, you must use language your readers or listeners will understand. If you need to use terms that will probably not be understood, you should explain those terms.
There is only one valid test of written English. If your readers easily understand your message exactly as you intended that it be understood, you have communicated effectively.