I'm defeated! Holy Cow this was one tough mother. I took this along for a normal in-between testing puzzle and wanted to pull my hair out. But at the same time, I simply love it. The idea is so simple. Calibron 12 is a puzzle consisting of 12 pieces. Just pack the pieces in the tray. How hard can that be right? ( Déjà vu I hear you say?)
I have this one permanently in my testing bag for those times when I want to feel like a complete idiot. Who knows, one of these days I may just solve it!
A video of it I have made.