Antique Jewellers Style screw driver. Question

[Ngarrett2]

Here are a few photos of an old Jewellers style screw driver made of iron and a little more robust than most Jewellers screw drivers.  Question   it has a slot that is half the depth of the circular shaft.
Anyone know what the purpose of this slot is?

[lptools]

Hello, Ngarrett2. This looks like another mystery tool, only the maker may know its intended use!! Jewelers are usually quite skilled, including machining, so I believe they made, or modified, a lot of their own tools. Regards, Lou

[wvtools]

I cannot tell from the pictures, but I have seen screwdrivers like that where the top end of the shaft of the blade was exposed.  You could put a small drift in the slot to pop out the blade and use a different size or style one.