The Altimeter; The single device that tells a pilot how high the aircraft is, and when to go missed on an instrument approach. There are many things that can cause the altimeter to be out of tolerance, Scale error, baro scale error, friction, case leaks, can give the pilot the "wrong" altitude. These rules have been in place for decades, and they are needed to keep the rest of the aviators in your airspace safe. New technologies are being installed into aircraft to provide a safer level of flying than we have ever known. All of this means that your airplane, and the equipment in it, needs maintenance. That maintenance is every 24 calendar months, or whenever a problem is brought to your attention. FAR 91.411
I picked up 08Romeo at Red Eagle Avionics, she passed with no problems. I got to jump in the plane and taxi around the airport before and after work. I would rather have been flying but any left seat time is fun!