# 5-Step Process to Checking Engineering Calculations

Checking engineering calculations is a big part of every engineer’s work. Because even the best of the best engineers make mistakes.

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 damage through my many years of design work.

I’m going to go over my 5-step process and 12 tips for checking engineering calculations. Use what you learn to catch mistakes in all levels and types of engineering. Before we get started 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 the Swiss Federal Institute of Technology in Zurich. The below-listed failures led to the death of 504 people and millions of dollars in damages!

Cause of engineering structural failuresPercentage rate of occurrence
Insufficient knowledge36%
Underestimation of influence16%
Ignorance, carelessness, negligence14%
Forgetfulness, error13%
Relying upon others without sufficient control9%
Objectively unknown situation7%
No clear definition of responsibilities1%
Choice of bad quality1%
Other3%

It’s a hard pill to swallow. But engineers could’ve prevented many of these failures through proper calculation checks. 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 calculations. You want a reader to have zero questions about your calculation decisions. Plus, after several years of not visiting your sheets, you’ll forget the calculation.

Next, add notes to your calculations. For example, the following are the types of notes I add:

• References: the source of information. For example, the textbook where I gathered data from.
• 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 following 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.

I always review my calculations multiple times. With each pass-through, I add more 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 you go through your writing many times, does it becomes 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. Print your calculations with space for comments.

## STEP #4: Backcheck the reviewer’s comments

After the reviewer completes their review, review their comments while sitting alone. This way you’re not directly influenced by the reviewer.

Check if their comments make sense to you. You do NOT need to agree with everything though. 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 their comments you don’t agree with. The goal of the sit-down is to reach an agreement on 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 calculations.

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. Also, 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 asking for help.
• Research the calculation 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.

EventIncident YearWhat happenedCause
The Hyatt Regency walkway collapse1981Suspended walkways on the second and fourth floors collapsed killing 114 peopleDoubling the load on the upper walkway connections without adding additional structural support
Gulf War patriot missile failure1991U.S. missile failed to intercept an Iraqi missile, thus killing 28 soldiersArithmetic programming error in calculating and measuring time
Explosion of the Ariane 5 rocket1996Exploded 40 seconds after liftoff, costing \$500 million dollarsSoftware error in the inertial reference system
Loss of Mars orbiter spacecraft1999Lost in space costing NASA \$125 million dollarsDue to wrong units being used; English versus Metric units
Tokyo Disneyland’s Space Mountain derailment2004 Roller coaster car derailed because of broken axleAxle broke because of conversion error from English to Metric units
New Orleans’ levee system2005New Orleans was flooded killing 1,833 peopleStrength 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.

This will allow you to 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 100 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. 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 unitsof measurement

Add units to your values. This is a good way to know if you’re even using the right equations. Also, units are 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. This is why you 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. Also many times, you’ll miss deadlines with bleeding-edge engineering work. This is okay and frankly typical.

### #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 structural design can probably hold a given load. So they don’t review their work.

Regardless of what you think you know though, 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. Then ask them questions about other parts of their design too.

If any of their replies sound strange, dig deeper 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 to not 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 by 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 work, engineers crank out.

Also, the more calculations you do, the easier calculations become. But this doesn’t make you bulletproof 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 of 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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