so you should split your arduino line by the ‘\t’ to get a string array,
and convert that strings to int.
but the arduino code not makes sense,
you read 0 … 1023 and create int -10 … 10
that are 20 steps only // you damage your resolution.
why not make them float in arduino and send float?
or much better just send the 0… 1023
and do the rest in Processing!