Understannding the rules, the conventions

This morning, I had to phone in a prescription refill to our pharmacy (CVS). They have an automated system that allows you to enter a number associated with the prescription, which makes the process pretty simple; simple up to one point, at least for me.

My wife is picking it up, and said she'd do so around noon. The pharmacy's automated attendant asked what time, and I entered "1200." It then asked if  this would be AM or PM. That's when I had to pause.

Recall that:

• AM = from the Latin ante meridiem, meaning "before midday"
• PM = post meridiem, "after midday"

[source: Wikipedia]

Since noon is THE meridian, it is neither ante nor post; it's just "meridian." Noon is 12:00 M. And so, I turned to my wife, who is less picky about such things, for help, and she said "PM." This worked, so the prescription will be ready at the appointed time.

However, 12:00 noon is definitely NOT PM; 12 midnight is. But, we (everyone but me and others who take this too seriously, actually) think of 12:00 midnight as AM. However, it isn't AM until one second after midnight.

Wikipedia offers the following: It is not always clear what times "12:00 a.m." and "12:00 p.m." denote. From the Latin words meridies (midday), ante (before) and post (after), the term ante meridiem (a.m.) means before midday and post meridiem (p.m.) means after midday. Since strictly speaking "noon" (midday) is neither before nor after itself, the terms a.m. and p.m. do not apply. However, since 12:01 p.m. is after noon, it is common to extend this usage for 12:00 p.m. to denote noon. That leaves 12:00 a.m. to be used for midnight at the beginning of the day, correctly, continuing to 12:01 a.m. that same day.

The 24 hour clock, which I became intimately familiar with in the army, makes this much simpler. Noon is 1200; midnight is 2400. We don't worry about "AM" or "PM." Midnight, being 2400 represents the end of a 24 hour day. One minute after midnight is not 2401; it's 0001. 

Sometimes our rules are confusing, sometimes they're just plain wrong, but we must conform, despite our objections, to doing so, in order to "get along" (or to get our prescriptions filled properly). 

In performance measurement we often deal with rules that make perfect sense, while at times we deal with ones that are not so clear. Sometimes, what appears confusing is only a reflection of our ignorance. This often happens when working with time-weighted returns, when there's a loss but we show a positive return: the typical and understandable response is "it doesn't make sense." And, it doesn't; until we get a better grasp of what is occurring. 

We can fight some of the rules, as I often attempt, or just give in. 

I am not the only one who has challenged the 12:00 noon is PM  convention; occasionally articles are offered on this subject, and these articles appear to only appeal to folks like myself. 

As a purest (I guess that's what I am), I also challenge calling a lectern a podium, or to suggest that "the lion's share" means "most" (it means "all"). But one can tire and frustrate others (such as my normally very patient wife) by being pedantic, so I will stop now. Hopefully my link to our profession is clear.