can a op amp be used for simple direct set point control for 0 to 10vdc signals. basically i am thinking + input is 0 to 10vdc signal and - input is a 10K pot. now the signals would need adjusting so the output is 0 to 10vdc but based on the 10K pot. so if the pot is at say 5k or half way and the + input is at 3 volts the output would go to maybe 7vdc conversly if the 0 to 20vdc input was 7 VDC the output would go down to 3 VDC. so as the input goes higher the output goes lower. have i got this right? is there a bettrer way? all thoughts welcome.