My pile of outgoing postcards usually contains addresses to Europe, Asia, Canada, etc. and the United States (where I live). When adding the date and temperature, I use metric measures for all but the US. But I rarely see imperial on cards I receive.
So, a Simple Poll:
0 voters
I cannot keep things simple, sorry. 
I usually tend to write the date the way of recepient does, sometimes I write it in Czech and that particular language (e. g. Czech - French). I have found that this is very limited to my knowledge of the recepientsā habits, because there are much more ways how to write day (and I am not talking about other calendars)
I do not usually mention weather / temperature unless recepient ask for. If he/she does, I usually write it in degrees Celsius, in case of the US I use both - degrees of Celsius and Fahrenheit. But honestly, I have never explored which countries use Fahrenheits - is it just US?
Sometimes
Yes, I always write date and temperature in recipientās country format, unless Iām not familiar with it. I use Ā°F whenever I send to the US.
And I use several ways to write the date :
*Month Day, Year ā to USA
*Year-Month-Day ā to China, Japan, Korea, Taiwan
*Day-Month-Year ā to Europe, Asia, Canada
But I usually write the month name and full year to avoid confusion (like: 12 APR 2023).
I try to write things in both, not only is it convenient for pretty much everybody, but also it helps me to learn the other units of measurement, I have learned that comfortable temperatures (around 68F to 72F range) is somewhere near 20 Celsius.
For dates, I always go with a thing like āAPR 11 2023ā instead or the confusing numbers and slashes because even I cant figure out what system we use, and it makes sence to most people once again.
According to ISO 8601, the standard format for dates is YYYY-MM-DD (year-month-day). Unfortunately it is not widely used in Europe & America.
@crazyseth I noticed the mailbox next to your nameā¦ how did you add that? ltās cool!
Yes, I tend to write the Imperial or Metric according to the country I am writing to. I also learned the āComfortable rangeā of temperature in Celsius. 
I use what I use normally, sometimes adding temperature also in Fahrenheit, but very very rarely.
The reason is, the card is from me, from my culture, my habits, and they see it in how I write date, temperature, distanses etc too 
Normally I write the month in words, so for example: 12th April 2023
I write the daily high and the low in Celsius unless they are a United Statesian, and I just write out the date to avoid confusion. (Iāve never had Myanmar or Liberia, but my point is I can translate the forecast looking but I donāt understand when I receive Celsius temperatures except I think 20 and up is warm)
I always write them as they are written in Finland. Day-Month-Year and temperature in Celcius. Or alternatively; April 12, 2023.
I tagged you in the forum thread that explains how to add emojis next to your name.
On my postcards I usually write the date with the month written in letters: 12. April 23. But normally I would write 12.04.23.
If and when I write temperature, I write it in Celcius because thatās what we use here.
If I receive a postcard from the US and they write the temperature in Fahrenheit, I donāt mind taking the time to look it up if I need to. But Iāve been to the US several times now so Iām familiar with the approximate conversion into Celcius 
For me, writing things like this in the way the sender would do in their country or culture, makes me feel like the postcard is even more personal, maybe I get to learn something new. For a person who is new to Postcrossing, they might learn that in the US you write the month first, or that in Norway we use kilometers (not miles) to measure the travel distance.
I always write the date as day.month.year but I write the temperature in F when sending to the USA. I used to write it always in C but then I received a card from the USA written in C and I thought it was really nice and convenient that the person already translated it for me. So since then I do it too.
Itās all about sharing information of origin of card, so Receiver will definitely appreciate thr local measurement unit and will like to do more research on it
In my opinion, if like to receive the information based on how the sender would write it as it is local to where theyāre from. It makes me excited to translate/convert that information to my local units which can be quite fun too
I always write out temperature in celsius since most of the world uses it. As for date, I spell out the month (so thereās no ambiguity), then day, and year: April 12, 2023.
Itās interesting to see many reasons for writing format here. I think it is also great to show our own culture. 
But at the same time I also think ā especially for temperatureā, it would help the recipient āconnectā with the sender more quickly and understand the difference in the weather at one glance without having to look up again. Itās a trivial information that most people only see for no more than a few seconds after all. It also might be easier for other people (like family or friends) to read them or if the recipient re-reading them someday.
When organizing my received postcards, I often re-read them more quickly and canāt picture how cold/hot is in the US at the time. And I sort the cards by their sent dates (if available), so sometimes I got confused by the date format.
But like I said, it is a light-hearted piece of information, so either way is good. Just enjoy!
And, my question was meant in a light-hearted way!
Thanks!
I also canāt keep things simple it seems! Iāve been writing my dates the āAmericanā way, MM/DD/YY or YYYY depending on space, but I think I might change to writing the day, month, and year (ex. 12 April, 2023) because I cannot retrain myself to write it in any other way. I write the temperature in Celsius on almost all sent cards now, even within the U.S.
If I notice a user is interested, I give them the temperature or other stats as measured here, in my native country. However, Iāve sent from countries whose systems differ, and in those circumstances change accordingly.