The perpetual calendar complication has been a fascinating and useful feature on high-end watches for quite sometime. Calendar functions directly related to keeping the time, and offer a variety of information related to the 24 hour cycle. Most watches have just the date, and the more complex you get, the more calendar functions you can record. Annual calendars measure the day, date, and month - often the phase of the moon as well. The benefit for those is being able to avoid adjusting your watch each month that does not have a 31 day cycle. Though there is still the matter of dealing with a 29 day February.
Perpetual calendars step it up a notch by taking into consideration leap years, which occur each four years and affect the length of February. Perpetual calendars are named as such because they don't need to be adjusted very often. The next time any perpetual calendar watch needs to be adjusted (by one day) will be the year 2100. This sounds sexy even though none of us will be alive to adjust the date. Of course, the humorous part to me is that this is all based on the assumption that your mechanical perpetual calendar watch will be running for that long (and in good condition). Still, having such a long range calendar feels reassuring - like the watch has got your back. For me, this complication is not only one of the most impressive to see on a dial, but also one that is functional (I am talking to you Equation of Time!).
If you want a watch with a mechanical perpetual calendar, you have a ton of options even though these are very high-end pieces. They come in a zillion varieties and many offer unique add-on complications such a year indicator, or week indicator, etc... If you are going to step into QP world (quantieme perpetual - another term of perpetual calendar) it is hard to know where to start. One good option is this classic, the A. Lange & Sohne Langematik Perpetual watch from a few years ago.
Available in gold or platinum, it has a 38.5mm wide case and an automatic movement with a 3/4 rotor (not quite a full rotor, but larger than a micro-rotor). The movement is the perfect example of why you should lust for an A. Lange & Sohne timepiece. It is good looking, highly complex, and includes much of what people are looking for in a high-end manufacture made movement. The balance cock is hand engraved while the automatic rotor is in solid gold.
Even though a perpetual calendar often displays a lot of information, the Langematik Perpetual Calendar organizes it well on the dial. The time and date are easiest to see. It features a big-date (which Lange calls an "outsize date") and easy to read lume covered hands. There subdials include info for the day, month, year, 24 hour hand, moon phase, and seconds for the time. It also has applied gold hour indicators and a timeless style to it.
A. Lange & Sohne has an excellent section on their website dedicated to the Langematik Perpetual that you can see here. One of the interesting things about the watch is that is among the few pieces Lange offers on a bracelet. Retail price for these Langematik Perpetual Watches is over $100,000 - but one (in platinum) is available on James List here for just under $70,000.