The 10 radio codes are a quick way to express meaning from a predefined table of meaning: 10-20 : where are you (what's your twenty?) this is often in movies' scripts 10-4 : 'understood' (what you said) the /10/ context allows to focus on what follows, and reduces the risk of errors in critical situation. Note: the worst airplane disaster ever (excluding war acts) happened on two airplanes crashing on the ground due to a misunderstood 'wait', during a short voice message from the control tower too one of the pilots (Tenerife airport, 1977).