From page 11-43 of the Installation Guide:
"Performing Transponder Checks
Manipulating Altitude:
If the test on your transponder requires manipulating the static pressure, be sure to manipulate static pressure only after activating SkyView’s pitot/static test mode. Instructions for using this mode are in chapter 5 of this manual. Pitot/static test mode is accessed via SETUP MENU > HARDWARE CALIBRATION
The SV-XNDR-261/262 can now be manually switched to ALT and GND modes: XPNDR > ALT and XPNDR > GND."
Note the key instructions are at the end of Chapter 5 of the install manual, page 5-22.
The system MUST be put in static system TEST mode to avoid creating problems with the ADAHRS when it sees vertical movement with no forward movement.
1. The aircraft itself should be temperature stable. For example, if the aircraft is moved from outside in the sun to a hangar for testing, tests should not be started until the airplane has stabilized at the hangar temperature.
2. Turn SkyView on and let it warm up until the altitude reading is stabilized. This period should be at least 5 minutes, but may take longer depending on environmental conditions.
To enter pitot/static test mode, go to:
SETUP MENU > HARDWARE CALIBRATION > ADAHRS CALIBRATION > PITOT STATIC TEST MODE.
Do not fly the aircraft while in pitot/static test mode.
When pitot/static test mode is active, both the active and standby ADAHRS (if equipped) are shown side by side to allow a single test to calibrated multiple ADAHRS. The airspeed and altitude values shown in this mode are the same as you would encounter while in-flight. They are not adjusted or otherwise altered from their normal readings and behaviors.
See related procedure:
SV-XPNDR-261/262 Installation and Configuration, Performing Transponder Checks.