Tag Archives: unit conversions

You can be part of the problem by being part of the Solutions

Being a former college student with an advanced degree in a “hard” science, I have a whole countertop of textbooks. I have also collected some that belong to related major and subjects through various agencies. In one particular textbook I found so many defective “solutions” I had to share them, for our mutual amuzement.

Before I start, I want to be clear: I know writing anything longer than a page is asking for errors and mistakes to slip in. To publish an entire book without mistakes is almost, if not completely, impossible. I am “featuring” this particular one because the problems are so severe that they should have been caught immediately by a competent reviewer or proofreader. They are mistakes that would be embarrassing to a student on a far lower level of knowledge, and in one case, are just weird.

Finally, I know the contents of the book are copyrighted by the publisher. I claim that my excerptions are “fair use” in the United States because I’m using them for critical commentary, in both senses of the word “critical”.

I found these in a solutions manual (teacher’s edition for college professors) for textbook intended to be used in a last-semester-last-year design course:


Wait, what? You can’t set a unit of mass equal to a unit of volume! That’s like saying “15 minutes = 4 watts”: it makes no sense!

What you CAN do is say “16 oz/16 floz = 1 pound/pint”. This is a statement of density, or how much mass a certain volume of a substance will have and is valid.

This is a particularly bad mistake since it, if used by a student, would cause a massive confusion about proper dimension/unit technique. Fortunately (?) it’s in a senior level textbook, so the students (and professor!) should know better by now.

This does bring up another question, this one for the author: Do senior level mechanical engineers really need a chapter to review unit conversions? (Personal opinion: if they do they were seriously mis-served by their previous professors)


Read this one a couple of times; I had to to figure out what on Earth was going on here. 1 furlong = 220 years?! The second sentence is a very valid question, the answer to which is, “they have nothing to do with each other”. I wonder if it was actually a proofreader’s query that got accidentally incorporated into the text, sortof like some very old Bibles. This needs to be thrown out or completely rewritten to not be an embarrassment to the publisher.


This is a legitimate question that deals with industry-specific nomenclature and units. That last sentence though… hardly a scholarly reference! And I note that they never did tell us what the metric system uses for can naming.


Yes, that is the ENTIRE answer.

Fortunately the book picks up after this bad chapter (which also includes other, less entertaining mistakes) and goes on to be at least usable for its purpose of providing senior level design problems and scenarios. Still, professor beware.