The pattern to get the cross is shaped 8-7+2 = answer is shaped 8

And the white pattern (last one at exit door) code shaped 5+1-4 = shaped like .
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(Press the upper panel on middle only and the left bottom 1st and 2nd from left only) there you go!!

Dear all , it is about the sign , not the number , like C+A-T = Something shaped like I I
So the rests are also the same, not the number itself but the shape of numbers! Good luck

Anybody could help me on level 23rd?? Stucked at clock code..