Telling someone to "Check 6" or "check it" is one of the most annoyingly stupid things in Aces High.
It provides no information, advises the pilot to do something he should be doing anyway and is plain bad advice if there is a real threat in your rear hemisphere.
It should embarass anyone that uses it.
Proper communication requires the following:
Identification, direction, information.
In other words, who you are talking to, what he should do, and why.
As an example, if I had a bandit (FW190) about to blast me to oblivion, telling me to "Check it" would only allow me to see the bandit that killed me.
Instead, if you say "Dawger, break, 190" you fulfill the requirements for good combat communication.
if the bandit is not an immediate threat one could say "Dawger, arc left, 190 long five o'clock". This tells me I'm not in immediate danger and gives me a suggested course of action.
If the nature of the threat does not require immediate action one may omit the directive portion but provide useful information. As an Example "Dawger, 190 long 5 o'clock" tells me there is a threat outside of guns range, where he is at and leaves me to decide how to proceed.
What information does "check it" give? It tells me there is a bandit somewhere in my vicinity at an unknown distance and direction. I must determine distance and direction myself and sort out exactly which bandit the call refers to in a multi-bandit fight. It is only useful to those completely without SA. Many times following the implied advice to look backwards will get you killed because you really should have been initiating a break turn instead of looking around for a bandit.
If I'm being chased by a 190 that I see and you call "Check it" I must decide if you are referring to the bandit I already know about or a new threat yet unseen. But if you call "Dawger, break, 190" I know you are referring to the bandit I am already aware of and don't have the uncertainty that the "check it" call brings with it.