Origin of the Balisong?

[RobT]

As a woodworker, I should have looked more closely at the pied du roy because I would have seen that the hinge is exactly the same as the main hinge on US and English box (or boxwood) folding rulers. A quick online search reveals that this type of ruler has been popular in the US and England since the early 1800s at least. The knife blade in the pied du roy example may have been attached for use as a handy scribe.
So, if I understand what has been said so far, we have three choices.
1) The balisong was developed in the Philippines independent of any outside influence. Note that the prior existence of similar blades outside of the Philippines doesn't preclude the possibility of parallel evolution.
2) The balisong was developed in the Philippines as a result of Filipino exposure to mechanically similar items such as a fan or a box rule.
3) The balisong began to be made in the Philippines after Filipino exposure to a balisong style knife that that had been made outside of the Philippines.

Sincerely,
RobT