The Hold button toggles between active and inactive states. If inactive the CV will pass through the device unchanged.
The Sample button is momentary and clicking it whilst Hold is active will “Freeze” the current value of an incoming CV signal.
When CV control is enabled, the device is in active Hold state when the [Hold CV Input] is a positive (>0) value and will trigger a “Freeze” when the [Sample CV Input] is given a signal that crosses from a value of 0, to any positive value.
When MIDI control is enabled we can use any white keys to toggle the “Hold” active / inactive state, and with the black keys we can trigger the “Freeze”
A logical “or” relation exists between the UI, CV and MIDI controls. For example if the “Hold” button is manually active on the front panel, it cannot be made inactive with a white piano key, but you can trigger a “Freeze” with a black key.