HP Calculator. How do I turn off "OCT" on my HP calculator please?

Your problem is that the calculator is in Base N calculator mode (Octal, base 8). only the keys 0 to 7 are active. Change the mode to Decimal (base 10) or reset it completely, and your calculator will come back to life.

There are two separate issues here.

Your calculator is in Algebraic mode. To switch to RPN, press MODE 5 .

Your calculator is also in Octal mode. To switch to Decimal, press right-shift 1 1 .

You cannot do it with this kind of calculator. You need a financial /business calculator.
There are 174 days.

OCT and Degree have nothing to do one with the other. Your calculator is in the Base-N computational mode. You have to change it to DECimal. Look for a key that has DEC marked next to it. You might have to press the SHIFT, 2nd or 2nd F key first.
Once the calculator is in Decimal numeration (press 8 or 9 to see if the screen displays the number entered) change the angle unit from whatever it is now (radian or gradian) to degrees. It is possible that it will show the DEG indicator after you switch to Decimal from Octal.

I am sorry but your not disclosing the make and model of the calculator does not help.

Sorry but this calculator cannot do calculations in other numerations just decimal. To make sure examine the calculator looking for markings like BIN OCT HEX. If you do not find any (and you will not) then you can be sure that it does not perform base conversions.

Please use the following link to download the manual for your calculator.
http://www.devicemanuals.com/guide/Calculator/HP/HP-20s-Scientific-Calculator-Owner's-Manual-==TVRFME5UWTE=.html

Try putting in a new battery.

If you want to use degrees (to have a DEG appear on top of the screen) you must exit all base-N modes (bin, oct, hex, or pent if available) and set the calculator numeration mode to DEC, decimal (the usual computational moode). The other modes are appropriate for handling certain types of calculations with integer (whole) numbers.

this s very simple....jus press MODE button twice u will find BASE in that...then press 3...then u can convert all those operations wch u want to proceed...jus try and reply me if u hav any doubt in it!!!!

Try n cold start, reseting the calculator, introducing an wire in the back small oriffice in the calculator. It may fix the problem.

JC