# Monthly Archives: January 2016

## Mathcad Solution To XKCD Problem

XKCD is a great comic strip by Randall Munroe that takes a quirky look at the world of science. Randall recently posted a set of questions for a substitute teacher to pose to a math class that were interesting and attracted the attention of some problem-solving enthusiasts. Continue reading

Posted in General Mathematics | 2 Comments

## My Minnesota Accent

I am from a small town in Minnesota called Osseo. I had never traveled far from home until I finished my undergraduate work and moved to Ft. Collins, Colorado. When I arrived in Colorado, everyone that I met immediately knew I was from Minnesota – I had no idea that my accent was so strong. After living five years in Colorado, I also developed an ear for accents, and I also could pick out where people were from because everyone in Colorado was from somewhere else. Continue reading

Posted in Personal | 2 Comments

## Relative Sizes in Photographs Can Be Deceiving

I often see photographs that appear to show objects with different size relationships than we usually see. In Figure 1, for example, we see the Moon as nearly the same size as the sailboat. This happened because the sailboat is some distance from the camera and its angular extent is comparable to that of the Moon. Continue reading

## Computing List Price from BOM Cost

All engineers must be familiar with the basics of product costing. In this post, I will cover a common product cost model (Figure 1) and provide two examples that illustrate how to calculate the list price of a product given the product's component costs plus some corporate parameters, like average discount rate and required gross margin. Continue reading

## Engineering Documents Should Not Be Like Snowflakes

I had dinner the other night with a networking engineer who works as a contractor. He is known as a person who writes well, and he is finding that many of the companies that he works for are asking him to determine how their networks operate and to write down what he discovers. Continue reading

## A Quick Look at the Walmart Closings

I saw in the news that Walmart is in the process of closing 269 of its stores, including 154 in the US. I became curious where the US store closures were occurring, so I downloaded the closings file and generated a pivot table of the data (Figure 1). Continue reading

## Book Review: Against The Tide

I have been working my way through a number of management books lately. The best of the lot, Against the Tide, was written by Admiral Dave Oliver about the management principles of Hyman G. Rickover (Figure 1). Years ago, I worked for a retired sub captain named Ernie Fischer. He had a number of interesting stories about serving on a nuclear submarine and about Hyman G. Rickover, the man responsible for creating the modern nuclear navy. Continue reading

## Worked Calculation Example of Lithium Battery Capacity Versus Load

I frequently am asked to comment on data that other engineers send me. This morning I received some test data obtained from an engineer measuring the backup time of an Uninterruptible Power Source (UPS) containing multiple lithium-ion (Li-Ion) batteries. The engineer was disappointed with the backup time provided by this UPS and wanted to know if his test results were reasonable considering the battery capacity of the UPS. While there were numerous circuit parameters measured during this testing, the critical information was the battery voltage versus time. Continue reading

Posted in Batteries | 20 Comments

## Old West Cavalry Distributions of Age and Countries of Origin

When I was a boy, my father often told me stories of his grandfather, Louis Bauer, who was a member of the US Cavalry on the American Frontier. In fact, my father left my brother Tim the watch, spurs, and shaving cup that Louis used when he served in the cavalry. I used to wear the spurs for fun as a kid. Continue reading

## Derivation of Pejsa Point-Blank Range Formula

A reader asked me if I could work through Pejsa's formulas related to calculating Point-Blank Range (PBR). During my earlier review of Pejsa's work, I chose not to cover this material just because it was not some of my favorite material – taste is definitely a part of mathematics. However, it is not difficult material to work through, and I like to answer questions when I can. Continue reading

Posted in Ballistics | 2 Comments