does the symbole +- exist in arduino
like if tension - tension = +-0.02
tension - tension = zero.
Always.
Do you mean "±"?
No.
If you just want to print the symbol ±, find the appropiate code number which is correct for the characters you are using on the display device: A terminal emulator, the Serial-window or whatever you LCD display has. (standard unicode value is 177) To send it use the Serial.write() which sends the value without converting it into 3 letters "1", "7" and "7".
The Arduino does not have any symbols at all. It sends numeric codes to&fro - you other program chooses which letter to display - usually for the code 65 it will be a capital A.
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Does that "symbol" exist in any other language? Not that I am aware of, though it might exist in APL.