As I was in preparatory and engineering school, I used the old HP48G calculator that I tuned by increasing the built-in memory by soldering additional chips within the beast (lots of effort to save the few hundred euros they were charging for 128kb extensions). This calculator was exceptional, especially the touch of the key that would firmly resist pressure until they would press and make contact with a 100% accuracy. Then came the HP49G with rubber keys that were crappy and that almost had HP cut off its calculator line. Now they’re back for good and better then ever with 2 new high-end calculators (HP39GS and HP50G) of very good quality !