Checking engineering calculations is a big part of every engineer’s work. Because even the best of the best engineers make mistakes.
And a mistake can be as simple as a single misplaced decimal. This decimal can then throw off an entire design and cause catastrophic damage. Thankfully, I’ve learned how to prevent such damages through my many years of design work.
I’m going to go over my 5-step process and 12 tips for checking engineering calculations. You can use what you learn to catch mistakes in all levels and types of engineering. Before we go over the process and tips though, let’s go over an engineer’s responsibilities.
An engineer’s responsibility to ensure public safety
The engineering code of ethics outlines an engineer’s responsibilities. Where the main responsibility is to ensure public safety. No different than a surgeon whose responsible for caring for each of their patients.
To show the importance of public safety, let’s look at a study of 800 structural failure cases. The study is by a Swiss Federal Institute of Technology in Zurich. The below-listed failures led to the death of 504 people and millions of dollars in damage!
|Cause of engineering structural failures||Percentage rate of occurrence|
|Underestimation of influence||16%|
|Ignorance, carelessness, negligence||14%|
|Relying upon others without sufficient control||9%|
|Objectively unknown situation||7%|
|No clear definition of responsibilities||1%|
|Choice of bad quality||1%|
It’s a hard pill to swallow. But engineers could’ve prevented many of these failures through proper calculation checks. And this is one reason why many engineers advocate for engineering licenses. Because engineers would hold greater responsibility and there would be fewer careless mistakes.
STEP #1: Include all your math steps and add notes
Place yourself in the shoes of a reviewer who reads your work for the first time. How can you make the reviewer’s life easier?
First, show all your math steps even for simple problems. You want a reader to have zero questions over any calculation decisions you made. Also, after several years of not visiting certain types of problems, you’ll even forget details yourself.
Next, add notes to your calculations. For example, the following are the types of notes I add:
- References: the source of information. For example, if I reference a specific table from a textbook.
- Codes and standards: code sections I adhere to. For example, a section in the National Electrical Code.
- Variables: definition of each used variable.
- Processes: explanations over certain calculation decisions and assumptions.
As good practice, add your notes in a different color. This makes the following of your calculations easier.
STEP #2: Self-check your calculations
After you complete your calculations, wait a day or two. Then, review your calculations. With a fresh mind, you can more easily spot mistakes you had overlooked.
I always review my calculations multiple times. And with each pass-through, I add notes and any missing calculation steps too. Anytime I need to stop and think over something, it’s an opportunity to add clarification.
I compare it to writing. Your first draft will always have issues no matter how great of a writer you are. It’s only after going through your writing many times does it become presentable.
Important Note: set aside time for checking calculations in your design process. Nothing should ever go out the door without a thorough round of checking.
STEP #3: Give your calculations to a qualified reviewer to review
Find a reviewer who has equal or greater experience than you. Otherwise, it defeats the purpose of the review.
The following are pointers to consider to assist the reviewer:
- Explain your calculations to the reviewer before their review. Tell them what you’re calculating and if there’s anything unique about your calculation.
- Give the reviewer ample time to review your calculations.
- Tell the reviewer to add comments to your calculations. So, print your calculations with space for comments.
STEP #4: Backcheck the reviewer’s comments
After the reviewer completes their review, review their comments alone. This way you’re not directly influenced by the reviewer.
Check if their comments make sense to you. And you do NOT need to agree with everything. Maybe they made a mistake. In your review, write down anything you don’t agree with.
Reviewer discussion after the self-review
Discuss with the reviewer the comments of theirs you don’t agree with. The goal in the sit-down is to reach an agreement over the accuracy of your calculations.
If you can’t reach an agreement, bring in a third party. Another set of eyes will help resolve any disconnects. Because in the end, everyone needs to agree on all parts of the calculation.
Important Note: write down everything you learned after the review discussion. This way, you document all the important details you may later forget. You don’t want to waste future time relearning for similar calculations.
Longterm relationship with the reviewer
If the reviewers are senior to you, build a student-mentor relationship with them. This is a great way to speed up your learning.
Just don’t expect the reviewers to do the calculations for you from scratch. They’re only assisting you. But, don’t be afraid to ask what you may think are “stupid” questions.
Important Note: prepare yourself before asking for help by doing the following:
- Do as much of the work as you can before going for help.
- Research the parts you don’t understand. This way, you can better understand explanations from the reviewer.
STEP #5: Submit your completed calculations and take more notes
Submit your calculations to your client or boss. Then more times than not you’ll receive comments back. If the comments are substantial, you may need to go through steps 1 through 4 again.
In the end, the goal is to create the best set of calculations each and every time. This ensures public safety, which is at the forefront of the engineering code of ethics.
To further drive the point home, below is a list of large failures from simple mistakes. These are easily avoidable failures through proper review and attention to detail.
|Event||Incident Year||What happened||Cause|
|The Hyatt Regency walkway collapse||1981||Suspended walkways on the second and fourth floors collapsed killing 114 people||Doubling the load on the upper walkway connections without adding additional structural support|
|Gulf War patriot missile failure||1991||U.S. missile failed to intercept an Iraqi missile, thus killing 28 soldiers||Arithmetic programming error in calculating and measuring time|
|Explosion of the Ariane 5 rocket||1996||Exploded 40 seconds after liftoff, costing $500 million dollars||Software error in the inertial reference system|
|Loss of Mars orbiter spacecraft||1999||Lost in space costing NASA $125 million dollars||Due to wrong units being used; English versus Metric units|
|Tokyo Disneyland’s Space Mountain derailment||2004||Roller coaster car derailed because of broken axle||Axle broke because of conversion error from English to Metric units|
|New Orleans’ levee system||2005||New Orleans was flooded killing 1,833 people||Strength of soil not properly estimated, and flawed data used on land elevation|
12 Tips on checking engineering calculations
Use these 12 tips whether you’re doing or reviewing calculations.
#1 Master your engineering concepts
Understand the science behind engineering concepts. Because you can’t always rely on arithmetic checks alone.
In return, you can quickly spot calculation busts even when the math checks. For example, a calculation outputs the top speed of a Ford Mustang is 10,000 miles per hour. Right off the bat, you’ll know there’s a bust as a Mustang or any car can’t reach this speed.
#2 Verify your equations
Check if you’re using the right equations. Sometimes your arithmetic is right, but you used the wrong equation. This happens a lot when engineers don’t understand the science behind their work.
#3 Verify your inputs
Verify your equation inputs. If you use the wrong inputs from the start, your output will be wrong even if you did everything else right.
Make sure your inputs are accurate and reasonable too. Say you’re doing a ground grid analysis for a new substation. If someone gives you the soil resistivity from a site 10 miles away, your results won’t be accurate.
#4 Create a master file for all calculations
Documentation is a master record of calculations in one place for all engineers to use. The documentation becomes a great resource for maintaining and transferring knowledge.
So, once your calculation is complete and approved, add it to a master folder for other engineers to use.
#5 Include your units of measurement
Add units to your values. This is a good way to know if you’re even using the right equations. Also, it’s a great way to tell if your calculated values make real-world sense.
Let’s go back to our Ford Mustang example. Imagine your equation outputs the top speed of a regular Ford Mustang is 160 meters per second. Instantly, you’ll know something is off. But if the result was 160 miles per hour, it’d be much more believable.
#6 Check for significant figures
Be consistent with the number of digits you use in your calculated values. This will help with the degree of accuracy in your calculations.
Normally in engineering though, a lack of significant digits won’t lead to failures. This is because of the many safety factors used in designs. So, just be attentive to what you’re designing and the level of accuracy required.
#7 Realize all engineers make mistakes
Even 10x engineers make mistakes. And the more you rush your work, the likelier it is you’ll make a mistake. So, don’t rush your designs even with a deadline around the corner. Your client won’t thank you if you turn in a garbage design a week early.
When you create a schedule for your work, consider both design and review time. And many times you’ll miss deadlines with bleeding-edge engineering work. In the latter instance, it’s totally okay to have delays.
#8 Format your design notes
Neatly add formatted notes to your calculations. Then stick with this note format with ALL your calculations.
This makes all your calculations uniform and easy to follow. For example, with blue written notes, your eyes always know where to go for clarifications.
#9 Know your material
To do quality calculations, you need to know your material like the back of your hand. What I mean is, you need to know exactly what you’re designing. Then, how it’ll fit into the real world.
This highlights the importance of hands-on engineering skills for engineers. In return, you can do better real-world reality checks on your calculations. Do your results seem practical?…
#10 Never become lazy
I know in some companies checking engineering calculations is rare. Older engineers sometimes go by feel as they’ve been designing for 40 plus years. For example, they know a given structure design can probably hold a given load. So they don’t review their work.
Regardless of what you know, don’t become lazy. Especially if you want to stay out of trouble. By building good habits, you’ll sleep better at night too.
#11 Ask questions as a reviewer
As a reviewer, if you find calculation mistakes, speak with the engineer on record. Ask them questions on other parts of their design too.
If any of their replies sound strange, dig more into their design work. More than likely, you’ll find something else they did wrong too.
#12 Be careful when following an engineer’s math and logic
Be careful as a reviewer not to blindly follow another engineer’s math. You can easily duplicate their mistakes.
I suggest starting your review with the mindset the calculation is wrong. Then, scan their work for mistakes. Also, don’t rush through your review going through the motions.
“Checking Engineering Calculations” wrap up
Checking calculations is a critical part of engineering. It’s why we have such few failures in designs today. This is despite the high volume of design engineers crank out.
And the more calculations you do, the easier calculations become. But this doesn’t make you bullet-proof from making mistakes. Because if you do something wrong once and it works, you’ll make the same mistake twice. And then sooner or later you’ll run out of luck. So, don’t ever feel ashamed or rushed to get your calculations checked.
I bet engineers of NASA, Jet Propulsion Laboratory (JPL), and Lockheed Martin wish they’d done a proper review over the Mars orbiter. JPL used the metric system, while Lockheed Martin used the English system. This unit mistake led to NASA losing its $125 million Mars orbiter.
What do you think is the best way to check engineering calculations? How often do you check your calculations?
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Koosha started Engineer Calcs in 2020 to help people better understand the engineering and construction industry, and to discuss various science and engineering-related topics to make people think. He has been working in the engineering and tech industry in California for over 15 years now and is a licensed professional electrical engineer, and also has various entrepreneurial pursuits.
Koosha has an extensive background in the design and specification of electrical systems with areas of expertise including power generation, transmission, distribution, instrumentation and controls, and water distribution and pumping as well as alternative energy (wind, solar, geothermal, and storage).
Koosha is most interested in engineering innovations, the cosmos, our history and future, sports, and fitness.