Nowadays lots of people may wonder how to do arithmetic with pen n papers(or even the mental calculation). Though it's not a kind of age test, in the past people really could handle everyday arithmetic without electronic calculators(well, no handphones too).
Back to those older days, some students had the possession of a trusty and user-friendly, yet powerful tool: the slide rules. It operates without battery and can perform some scientific functions. How incredible!!
The picture shows part of my slide rules collection ( they were made mainly from China, Japan and West Germany). Some of them are even in mint condition.
Thank "Kan sir". The chat with him reminds me of the collecting of these gadgets.
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