I usually attend church at 10am on Sunday Mornings. I also like to give thanks in church on Thanksgiving Day. When I entered church on the 4th Thursday in November, 2009, I was disappointed, but not really surprised, to see that the time of the special service that day was printed on the bulletin as "12 PM". AGH!
No, I don't really expect younger folk to know any Latin, but I would expect them to understand that "AM" means "before noon" and that "PM" means "after noon". I have even seen 12 midnight shown as both "AM" and "PM". Yecch!
These solecisms would not be necessary if we adopted the 24 hour clock, which many of us learned in the Armed Forces. There is no ambiguity when one reads that dinner is served at 18:30. However, I despair of the English-speaking world adapting to the 24 hour clock within the foreseeable future. My sweetheart, who changed her name (admittedly with some reluctance) some forty years ago still occasionally asks me to interpret time, using the 24 hour clock.
These thoughts lead me to wonder why the USA is slow to measure distances in kilometers, etc. The metric system was, after all, long adopted for our currency, whereas until some time after I left the UK in 1957, we still measured our money in Pounds, Shillings, and Pence.
(The quaint term "Guinea", which used to be one pound and one shilling, is probably still in use in high-priced British establishment; however, if that is the case I really don't know whether that is pound 1.05, or something else.)
When I was growing up, the alternative to Fahrenheit was known as "Centigrade". That is, of course, now widely known as "Celsius". This system is widely known throughout the world, but we still stick to Fahrenheit in this country.
European regulations made it mandatory to scrap the names for traditional British weights and measures. I was glad to read quite recently that it is still permitted to order a pint of beer in a pub, but gone are the pounds and ounces of my childhood. At sea, a ship's speed is still measured in knots, where one knot represents one nautical mile per hour. This measurement is likely to remain, for navigational reasons with which I will not try to explain here.
On a slightly different topic, I well remember that when I took my car from England by ferry to the continent, I needed to change light bulbs for the headlamps, because in Britain we had to "keep left", and when we dipped out headlamps, the light shone on the left hand verge - which would have directed it towards oncoming traffic when driving on the right.
I believe that, at the end of WWII, when Petrol (gasoline) was strictly rationed, we missed great opportunity to change over to driving on the right side of the road. This would have been before we spent billions on the motorway system. In contrast, the Swedes made the switch, after due notice, in the middle of the night, with little or no major problems.