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Honing and shaving with it would be a pretty good test.
But odds are that if it came out of your Grandfathers collection/use it was made in the huge block of time in the mid 20th century.
If I...

I need to dig out mine...
But I think the Boker is a "King Cutter" and this is a "King's Cutter"

There where hundreds of razor makers in Solingen before WWII and they made razors (great shavers)...