Linear power-supply potentiometer feedback circuits

How to get a perfectly linear response, and protect against loss of wiper contact. Full details on my website at: http://imajeenyus.com/electronics/20160517_potentiometer_feedback/index.shtml Here's some situations where I've used this kind of feedback circuit: LM317 constant current source: http://imajeenyus.com/electronics/20160530_adjustable_current_source/index.shtml 40-400V power supply: http://imajeenyus.com/electronics/20111010_40-400V_supply/index.shtml Modifying SMPS for variable output: http://imajeenyus.com/electronics/20151028_smps_variable_voltage/index.shtml