A TSO is a TSO is a TSO.

Bill writes:

<<< It is not true that every other piece of equipment in an experimental aircraft must meet TSO.>>>

What I  wrote was " You MUST have at least one of each of the required instruments and they MUST meet the TSO, regardless of whether the manufacturer has TSO Authorization or the altimeter has TSO Design Approval."

Bills confusion is not uncommon. He is confabulating in an attempt to reconcile the functional requirements of a device with the administrative function of demonstrating that the device complies with the requirements.

I will try one last time to explain. If Bill still doesn't get it, then my powers of explanation are insufficient.

We all must agree that FAR 91 specifies the minimum equipment needed for VFR flight and that equipment includes airspeed indicator, altimeter, compass, fuel gauge, oil temperature, etc...

Now suppose an alien from Uranus lands at Bill's hanger looking to study this thing called "Airplanes"

Alien, "How do you know how high you are from the ground when you are flying this airplane?"
Bill, " We use an Altimeter"
Alien, "How does and altimeter work?"
Bill, "It measures the pressure of the air and converts that measurement to feet above sea level."
Alien, "I see , but there are many ways to measure your altitude. You could drop a stone and measure the time it takes to reach the ground or measure the angle to your shadow and calculate your elevation using the time of day and your latitude or your could use radio waves and bounce them off the ground or you could.."
Bill, "Yes, all that is true but we use pressure."
Alien, "I see but pressure on your planet varies over time, how do you agree on the altitude?"
Bill, "My altimeter has a barometric compensation adjustment that I use to correct for barometric pressure changes over time."
Alien,  "That is very cleaver Bill. Are all pilots as cleaver as you?"
Bill, " Yes, we all use the same type of altimeter."
Alien, "So all the pilots in the world got together and agreed on how to measure altitude? That is amazing!"
Bill, "Well no. We have a special sub class of humans called "Bureaucrats" and the bureaucrats got together an agreed on a standard that all pilots would use."
Alien, "So for all the different types of altimeters that are possible there is only one type with certain features that satisfies what is needed for an "Aircraft Altimeter"
Bill, "Exactly! You are one smart Uranusian."
Alien, "Interesting. How do these bureaucrats communicate their decrees regarding standardization?"
Bill , "The write them down and publish them for all to read and obey."
Alien, "What are these decrees called?"
Bill, "Technical Standard Orders or TSOs for short"

For an altimeter to be an altimeter is must meet the TSO for "Altimeter" but it does not necessarily have to BE TSOed which implies that the TESTING and Manufacturing of the device was reviewed by the FAA and approved.

If you don't understand now, I give up. I refuse to be reduced to using sock puppets. Seek professional help.

Regards
Brent Regan