Topic: I've played perhaps 750+ games and this never came up before.

[Vincent of Vega]

Sorry if my topic sounded like Clickbait, anyway, you're here now

In a battle last night, the protagonists are irrelevant. Something happened that I've never seen before or given any thought to.
As the way I've played it is the way absolutely every single one of my opponents over 17 years or so has.

In my opponents turn he was deciding who was going to charge, there weren't many and the few were quite straightforwards. Then he came to a unit of his which was at quite a funny angle to one of mine who he was contemplating charging.  He can't decide if my unit is in his arc of sight, I'd already looked across the diagonals of his bases and decided  they were not but he then gets out one of those angle checkers to check whether he could indeed see my unit. I (politely) say "you can't check, you have to declare a charge first and then check"  He was of the complete opposite opinion.   As I mentioned I can scarcely believe that this has never ,ever come up before .

What are your thoughts?  I can find nothing in the BRB to say you can check 'before' declaring a charge, it undoubtedly states that you can only charge something that is in the arc of sight of at least one of your models in the relevant unit.

Thanks
Alex

[The Black Knight]

Huh, interesting. I know I've often wondered if it is okay to check arcs of sight. It's kinda easier in 8th ed where the rules explicitly state you can measure anything at all times. But in 7th and lower... I personally don't know of any rules that would specify it.

[KTG17]

Well I am no expert but I would have to inject some common sense into it and allow for the measure. I already think the arch is a little ridiculous because people don’t blindly stare forward and they are going to see off to the side without even turning their head, let alone turning their head. But that being the case, they should know who they can and can’t see, so I say measure who they can see before they declare who they can charge.

I am surprised this hasn’t come up before, but then again I am still trying to make sense of two units coming together.

[Warlord]

Was it a friendly game? Whats the big deal?
You can only declare legitmate charges. If he declares that as his charge, finds its illegal because of angle, then he can declare another. Doesn’t mean he forgeits charging because it was an illegal charge. Is that what you were arguing?

[Fidelis von Sigmaringen]

8th edition BRB p. 16: "When you declare a charge, one or more of the models in your unit must be able to trace a line of sight to the enemy unit, and the target must lie at least partially within the charging unit's front arc." Furthermore, a " unit cannot declare an impossible charge."

So, to declare a legal charge, the target must lie at least partially in the front arc. Since this is a precondition to declaring a charge, that means you are allowed to check, because otherwise you might be declaring an illegal charge, which you are not allowed to do. 

The rule as such has not changed between 6-8 the edition, although the wording has. Edit: However, in previous editions, you were expressis verbis not allowed to measure distances, while in the 8th, you are specifically allowed and, indeed, sometimes required to measure distances, since you cannot declare charges against a target that is outside of the chargers' maximum possible charge range.

[Vincent of Vega]

A few points. You absolutely can declare an illegal charge. If you are out of range after having declared a charge then you have a failed charge. It's a hugely important part of the game. Baiting someone to make a charge you believe is too far away and therefore having that unit sat in front of you subs games.
It was a friendly game so it made no difference and also the game was already over as a contest so whether he charged or not was irrelevant.
 Common sense is all well and good but there are numerous instances in the game where there a set rules which on a real battlefield simply would not happen but they're there to make the hands work.
My entire point is that I cannot find anything in the rule book that says you can check arc of sight before declaring a charge. Equally, is doesn't state that you can't.   
I've always played it that you can't check and you have to use your judgement just like when you have to assess the distance of the charge.

[Fidelis von Sigmaringen]

I see where you go astray.  A failed charge is not an illegally declared charge. You are absolutely not allowed to declare illegal charges. However, legally declared charges can result in a failed charge.

As I pointed out in the edit above (which crossed your post), there is a difference regarding charge ranges between editions. The baiting you refer to is no longer allowed in the 8th edition. The previous editions did not have the additional requirement that the target must be within the maximum possible charge range. So, you could declare a charge against a target that was not within the maximum charge range. However, these editions had the same requirements for declaring a charge that the target must be within LoS and frontal arc of the charger. If the target is not, you simply cannot declare a charge. So, if it is unclear, you must check.

[Vincent of Vega]

I should have said this game was a sixth edition game .
You cannot declare a charge that is obviously out of range is what I think it states in the BRB.
I appreciate you can't charge things you can't see but I can see anywhere where it states you can't declare a charge at something you think might be out of Los.
Ultimately , if you are allowed to check then so be it, but I'm obviously very surprised that until Monday evening not one single opponent had checked .

[Fidelis von Sigmaringen]

It does not need to, because the rules specifically state that you can only declare a charge against target that you can see, i.e. within LoS and frontal arc (unless, of course, specifically stated otherwise.)

6th edition BRB p. 44: "A unit may only declare a charge if at least one model in the unit can see at least one enemy model in the opposing unit.[...] The exact rules for Line of Sight can be found under Facing (page 41). "

Note: this is translated from the German version, and the exact wording may be slightly different in the English version. 

The pictures with examples on the same page tell the same story.

So, being in the frontal arc is a precondition for declaring a charge. If you do not meet this precondition, you cannot declare a charge. In most cases, it is clear whether the condition is met or not, and there is no need to check. In those cases where it is unclear, you must check whether you can declare a charge or not. I mean how else would you resolve a dispute where one player says the target is within the frontal arc, and the other says it is not. In the 6th (and 7th), being in range is not a precondition for declaring a charge, but for resolving the charge. Perhaps this has confused some players.