Since we have had this range/oven, the oven has consistently burnt baked goods (biscuits, cookies, etc). Although we have made adjustments, the results were inconsistent and unsatisfactory. I noticed that this model has a setpoint adjustment but I have lost the owner's manual and was only using the service tech bulletin in a pouch behind the range controls.

My initial reading with the oven set for 350F was ~375F with a kitchen oven thermometer (bimetalic strip type). I set the adjustment for -20F and tested again; got a 400F reading. Thinking that I had "gone the wrong way", I adjusted the setpoint for +20F; new reading 450F. Final test was at -30F resulting in a 400F reading. The adjustment is from -30F to +30F in 10 degree increments. The readings were taken after a minimum of 10 min after setting the temperature but the oven was not allowed to cool between tests.

Am I doing something wrong? Why only a +/- 30 adjustments?