Measure this rig's built-in A/V skew against the reference device (an LED that ramps bright + a piezo, fired at the same instant). The analyzer then subtracts it.

• Dim the room · put the phone ~30 cm from the device · quiet room
• Reference device in SWEEP mode, ramping every 2 s
• Tap Start, then tap the LED in the preview to place the ROI
• Steady + exposure locked? Tap Reset — the count restarts from clean events
• Watch pairs accumulate — Save unlocks at 8 clean pairs