so if the chars sent are 45x (turn x servo to 45 degs)..
v is the value we want to send to the servo and it is currently 0
The first char (ch) is 4 so
0*10 = 0 + 4 - 0 = 4;
Second char is 4;
4*10 = 40 + 5 = 45 - 0 = 45;
Third char is not a number(0-9) so we drop through...