What's the etiquette for greetings on video calls?

When you meet face-to-face, you can start with “good morning” or “good afternoon”. This can be achieved with a subtle check of your watch, or some convenient clock, or even — and I’ve heard of people doing this — actually looking outside to see where the sun is.

But when it’s a video call (or even a telephone call) where the other person is in a different time zone do you still say “good morning” (because it is your morning) or should you say “good afternoon” (if it’s their afternoon)? What do you say when you join a call with people in many different time zones for whom it might even be the middle of the night? Is the appropriate thing to do to keep an almanac of all the world’s timezones on hand (including Summer / Winter daylight savings time changes), so that you can give the right greeting?

And on that, is there a way of subtly emphasising that you had to get up at some ungodly hour (like 8:30am) to make the call at a time convenient for everyone else? Is this a situation where you should deliberately put the video on so that everyone can see you are still in your pyjamas, or is that a bit too unsubtle to get sympathy?

Looking on the bright side

Since 2007, even in boom times our emissions have declined, just very slowly.

During times of recession though, Australia's greenhouse gas emissions decline more quickly (e.g. 1991-1992).

So would a long protracted covid-19 recession get us on track for the Paris accord?

How I teach classes remotely

I’ve been teaching classes remotely for over a decade now — mostly to adult learners — and so I thought I’d share what I’ve learned. With a lot of schools and universities having to switch to remote classes, here’s what I can suggest:

• One of the most useful tools is Krisp.AI. (Affiliate link to get one month free: krisp.ai ; link for the free version for students and educators https://krisp.ai/blog/covid19-response/ ) — this automatically removes background noise, so you can be delivering a class in a noisy coffee shop and it sounds to your listeners like you are in a quiet recording studio. It is free to students and educators at this time.
• The second most useful tool is a good quality microphone. I use the Blue Yeti (affiliate link Blue Yeti ; direct link https://www.amazon.com/Blue-Microphone-Silver-Certified-Refurbished/dp/B01LX1N2WT) and it is very, very good. You can then use cheap earphones to listen, because the Yeti has a good phone-out audio monitor.
• If you have a modern laptop, you can use it to remove the background behind you automatically. Otherwise you can make a green screen very cheaply: (affiliate link: tension wire, direct link https://www.amazon.com/gp/product/B07P3KQYGV ). Either way it means that you can run a class from your bedroom (or wherever) without much invasion of privacy.
• If you are presenting a computer desktop (e.g. I teach programming classes, so I do a lot of this), then get your IT department to organise an Amazon Workspace for you. Join the conference call twice — once from your laptop, and once from the Workspaces session. Share the Workspaces screen, not your home laptop. That way, if a message pops up on your screen, the students won’t see it.
• If you are low on bandwidth (which shouldn’t be the case in Australia, as Optus and Telstra have lifted their link speeds for everyone), you can use Workspaces & phone in to the call. Your telephone voice has priority over data, so your voice will be clear and crisp. Your Workspaces computer will never be affected by low bandwidth.
• Remote classes scale up better than face-to-face. It is a brave teacher who would be willing to teach a 60-person face-to-face, but it can be done remotely. So ideally, pair up with another teacher teaching the same class at the same time: one of you will deliver the lesson, and the other teacher will handle audio muting, responding to comments in the chat channel and keeping the class on track. I’ve generally done this with a model of senior instructor + junior support teacher.
• Depending on the class, you can do open-mike for everyone, or otherwise do a structured question asking: e.g. if you want to ask a question, flag in the conferencing tool, or ask the question in the chat channel. Then your support instructor can interrupt the class with the question.
• It is OK to watch a video (e.g. from Khan Academy who have got daily schedules organised) together, and then discuss it afterwards. It’s OK to admit that there is a resource on the internet that can be better than you at explaining something through a computer screen.
• You need to have some kind of “exit tickets” from each lesson (or at least each week) where students tell you what the lesson was about, and any questions that they have. It is often quite enlightening.
• The chat channel in Zoom and google hangouts doesn’t quite work; but they are definitely the right choice for running the video session as you can mute participants, create breakout rooms and so on. Slack or Discord can work better as a chat channel, particularly if you have a co-instructor monitoring it for you.

HSC General Maths questions

Every year the HSC General Maths exam in NSW has some question about a roof with rainwater and a cylindrical tank to hold it in.

I just created three sample questions (with worked answers) if anyone else has students / family / self wanting to get some practice questions that aren't already in a past paper.

https://gum.co/QnbuQ

What's happening to the rain in the city of the endless summer?

I hear that my friends and colleagues in the USA are having a cold winter. Could we swap? We've got enough heat to spare this summer.

I've started pining for the cold season -- April to September in Sydney.

I remember the "cold season" from my childhood having sport cancelled a little bit more regularly than it is for my children. By the way if anyone else from my soccer team is reading this, do any of you remember us ever scoring a goal or winning a game? Maybe we didn't practice enough.

Anyway, I don't remember the droughts being as bad back then either.

So how much less rain are we getting?

Looking at the left-hand graph, it's a very noisy signal, so I went with a Theil-Sen regressor to try to find a good trend line. Theil-Sen should be more robust to noise than using ordinary least squares regression. It's not super-accurate, but roughly 0.6mm per year looks about right. 30mm difference since the 1960s is roughly 5% less rain. That sounds (and looks) about right.

Normally I wouldn't want to do a 50 year rolling average on a data set that only goes back to 1859, but anything much less than that and the trend wasn't very clear. Even using a 50 year trend (the graph on the right) it's still quite lumpy.

So what's going on? Is it raining less heavily than it used to?

Nope -- that's the opposite of what we expected. When it rains in the cold months, it actually rains harder than it used to.

In 2001, a typical cold-season storm dropped 8.8mm of rain. The median rainfall on a rainy day was 8.8mm. In 1901, a typical storm deposited just 2.8mm.

So is it raining less often?

Yep -- a lot less. Winter drought is a serious thing now. Back in 1891 it rained for 120 days (out of the 183 days in what I call the "cold season"). Last year (2018) it was 50.

Out of the top 10 driest winters (fewest days of rain), 4 of them happened since 2000; and if we discount the extremely dodgy-looking measurements from 1858 (the first year the Bureau was taking measurements) then 5 out of the top 10 have occurred since 1995.

(Silly extrapolation: the regression trend suggests one less rainy day per decade. 2409 will be on track to have no winter rain at all. I think that would make Sydney into a desert.)

Droughts are getting longer (through winter and summer), and then when the drought breaks, we get smashed with a deluge of rain in a short burst. Winter wasn't like this when I was younger: ask some older people about their experiences too. It was just regular constant drizzle.

Summer rain patterns are more complex, and I'll do a post about that another day. Preview: summer rain isn't solving the winter drought problem.

If anyone wants to do Melbourne (the city that rained that little bit more than Sydney), I've put the jupyter notebooks on github here: https://github.com/solresol/endless-summer/blob/master/rainfall.ipynb