Cessna-180 pilot reported while showing a passenger some different functionalities of the avionics system; the altimeter Baro was accidentally changed. The pilot reports the aircraft altitude may have gotten lower than the FAR's allow.

Narrative

On a flight from ZZZ to ZZZ1 on Day 0; I was flying north along the river; The altimeter was set to the reported AWOS at last airport I had passed. After passing that airport I was showing a passenger some functionality of the avionics system and inadvertently adjusted the barometric pressure changing my displayed altitude. I did not notice that change as I was looking to see was something different when the adjustment of the knob was made. I thought I was changing the heading bug but it was not moving; The multi-function knob on the primary flight display was set to BARO vs. HDG. Shortly after showing this functionality; we were descending to a lower altitude. Because of the inadvertent change in barometer setting; my altitude over the ground (river) may have been lower than I wanted based on the altimeter setting. During the decent; I set the Altitude bug to an altitude that would of been several hundred feet above the 500 foot minimum altitude per CFR 91. This is a great function of the system because it provides a 'leaving Altitude' aural warning at +/- 200 feet. Because of the inadvertent change to the barometric pressure; we were lower that expected and there should of been an aural warning indicating I was lower that planned. I noticed we seemed low; applied power; and gained altitude; received a new ATIS from ZZZ1 and noticed the BARO was off by quite a bit. It was adjusted to the corrected to the proper barometric pressure and we continued to a landing in ZZZ1. After the landing I reviewed how this could of happened and narrowed the mistake down to the multi-function knob and the event noted above. To mitigate the risk of the inadvertent change of altitude in the future I have eliminated using the optional 'BARO' functionality from the multi-function knob on the primary flight display. This has reduced locations I will change the altitude from multiple areas and reduced it to only two. The 'BARO' knob and the touch screen on the primary flight display. Both of these are specific to the BARO adjustment and not a multi-function change. Adjusting with the he touch screen; it is very evident you are making a barometric altitude change and not something that can be accidentally changed. The other is the BARO knob; that knob is in a location that is specific to making a change to the barometric pressure and is not a multi-function knob. Several other steps that have been implemented is when changing the BARO; verify altitude on the STANDBY indicator and also the GPS feed on the iPad. Another verification step will be prior to any planned changed in altitude the current altimeter settings will be verified prior to the altitude change on the multiple sources.