Not explaining each variable is bad practice, other than for very simple things. (I do expect everyone and their dog reading a process eng calc to know PV=nRT, at a minimum).

Just like (in my opinion) not defining industry specific abbreviations is also bad practice.

Mathematicians don't do this? Shame on them.

[–] [email protected] 10 points 2 months ago (1 children)

I mean, it was rather physics that was worse in this regard.

Mathematicians do define their variable quite rigorously. Everything is so abstract, at some point you do just need to write down "this thing is a number". Problem with maths folks is rather that they get more creative with their other symbols. So, "this thing is a number" is actually written as "∃x, x ∈ ℝ".

But yeah, in the school/university physics I experienced, it was assumed that you knew that U is voltage, ρ (rho) is density, ω (omega) is angular velocity etc..
At one point, I had to memorize six pages of formulas and it felt like every letter (Latin, Greek, uppercase, lowercase, some Fraktur for good measure) was a shorthand for something.

[–] [email protected] 3 points 2 months ago (1 children)

I should specify when I say physical engineering I just mean chemical, mechanical, electrical, etc. (not software), rather than physics in theory/academia.

I guess engineers are applied physics (in a particular area each), and we need to distribute our deliverables to people who aren't necessarily experts in every discipline.

It just also makes sense to always define variables.

It's so funny because I've never seen voltage defined as U, and not V haha, proving how if you're going to have an equation, you'd better define everything, there's so many reused letters!

Thanks for sharing

[–] [email protected] 4 points 2 months ago (1 children)

U is definitely standard for a difference in electric potential in Europe. Thought to come from "Unterschied", difference. V refers to electric potential, which as wikipedia says so wisely, should not be confused with a difference in electric potential. Which North American notation does. At least it's not PEMDAS...

[–] [email protected] 4 points 2 months ago

There ya go (only used it up until highschool physics, in Australia, iirc), I definitely have no business reading anything regarding voltage then 😅

Thanks for sharing

[–] [email protected] 4 points 2 months ago (1 children)

Still bad, i'm not a computer with a lookup table in memory.

I do expect everyone and their dog reading a process eng calc to know PV=nRT, at a minimum

What is "eng"?

[–] [email protected] 5 points 2 months ago* (last edited 2 months ago) (1 children)

Lol fair point regarding Eng: "Engineering".

But Nah, I think assumed knowledge of PV=nRT is fair in context, since if you don't know what it is, you'll only be reading the conclusion, not getting into the weeds of a calculation document.

I'm not going even going to be explaining if I have a column that's says volumetric flow rate, with V=m/ρ. If I give mass flow rate and density (with units, of course), and use these extremely common symbols, and someone doesn't understand, then they have no real business getting to this level of detail anyway.

I do agree that in most cases not defining your variables is bad practice, but there is some nuance, depending on the intended audience and how common a formula is, and the format of whatever it is you're writing.

[–] sukhmel 0 points 2 months ago* (last edited 2 months ago) (1 children)

So, in the end you just do assume everyone to know the "common sense" one-letter notation for everything. Well, not everything, but the essential ten thousands of entities for sure /s

This sounds like No true Scotsman fallacy to me

I find it a bit contradicting to the very point you made about defining variables. If anything, one might be some home-grown genius that has real business getting into details but only ever used Chinese characters as variables

Edit: forgot to set language

[–] [email protected] 2 points 2 months ago (1 children)

Understand your frustration with how I've communicated my position, sorry about that:

My justification for the examples I've given is there still needs to be other context, is based on complexity of the equation, and the intended audience of that equation.

An example of me not explaining a very simple equation would be perhaps a table of various cases:

Realising now that markdown tables don't seem to work 😅, hopefully this is still clear.

It may be a touch better to put variable symbols in the other columns, but:

You still have the final answer (the purpose of my report, I'm not writing a thesis here)
It should be plainly obvious by the units, and the fact those are the previous two variables, to someone who has the ability to understand (and is the intended audience of that little equation)

As a recent example for this, in a data sheet I recently prepared, I literally just put a * in the references column and said "*calculated from other data sheet values" for the volumetric flow rate, because the intended audience would know how to do that, and the purpose was for me to communicate how that value was determined.

Me putting in the V = m/ρ in the hypothetical example I gave above is a just a little mind jog for the reader.

Where more complicated equations are used, of course these are properly referenced, usually even with the standard or book it's come from.

I'll redefine my position to: Clearly define all variables, unless it's abundantly obvious to your intended audience from context.

My intended audience of the conclusions or final values are the layman. My intended audience of everything else is someone with a very basic chemical engineering understanding.

Your last point is a strawman:

I find it a bit contradicting to the very point you made about defining variables. If anything, one might be some home-grown genius that has real business getting into details but only ever used Chinese characters as variables

Because I'm writing in English, for an English speaking audience, and there is no such thing as a home-grown genius getting into my area because it's a legal requirement that they have an honours degree. Even still, the two assumed knowledge equations I mentioned, which I would only not reference with sufficient context, would STILL be recognisable with totally random symbols.

| mass flow (kg/hr) | density (kg/m³) | Volumetric flow (m³/hr), 容 = 质/密 | Yup, a bit odd in an English context, but with the units information (always mandatory, of course) completely understandable.

[–] sukhmel 1 points 2 months ago (1 children)

First of all, thank you for a thoughtful response, I was too snarky, sorry about that.

TL;DR: guess I'm just upset that there is no objective way of measuring how much knowledge is required, and trying to read everything from sources list would take forever.

Yeah, the last point is sort of a strawman, although I meant it not to highlight that explanations should be given in terms that the reader is used to, but rather that the reader may have quite arbitrary amount of prior knowledge.

I agree that there probably should be some shared context, what bugs me is that people tend to vary a lot in what amount of context is considered to be required. And more than once have I met papers that require deciphering even if you have some context and kind of come from the field they are written for. I used to think that this is our of malice to make reproducing their work harder for others, but maybe it was just an assumption of much larger shared context.

Tables markdown work in some clients, afaik, but I don't remember which, and even if I saw it or imagined it

[–] [email protected] 2 points 2 months ago

No worries friend, no hard feelings and appreciate the engagement!

Yeah, agree it is a bit wishy washy in terms of gauging how much explanation to include ¯_(ツ)_/¯

I suppose (in my opinion) the mindset should be: include as much explanation as possible, without it being cumbersome.

I personally err on the side of over-explanation and have had some senior engineers give me feedback that it's too much. Still learning for myself how much is too much.

Totally agree though, that there are many cases where people leave things out as assumed, when it's not really reasonable to do so.

A side-thought on specificity: one of my biggest pet peeves is when people list pressure with the units of kPa, when they really mean kPag. In industry, you are rarely talking in absolute pressure (other than for pressure differences) and people then get lazy/don't know/assume it's fine to do something like: set point 100 kPa (when they mean 100 kPag). It isn't fine though, because at lower pressures atmosphere counts for a pretty large percentage of the absolute value.

[–] [email protected] 1 points 2 months ago (1 children)

What's PV? Asking for my friend's dog.

[–] [email protected] 2 points 2 months ago

(Pressure) * (volume) = (# moles) * (gas constant) * (temperature)

The ideal gas law.

In another thread I admit I didn't explain my position here well enough. I would only not explain this equation given sufficient context (e.g. I've shown all those variables in a table, and my intended audience is people familiar with basic chemistry, which I'd expect would be everyone reading the report for this particular example, since this is high school chemistry, and the topic of all reports I work on is chemical engineering.)

People can read the conclusions if they're not familiar with chemistry, and for the detail, they're not my intended audience anyway.

Generally I still hold the position that you should define variables as much as possible, unless it's overly cumbersome, given your intended audience would clearly understand anyway.

In context this simple equation is obvious even if you change the symbols, as long as there is sufficient context to draw from.