Reforms and the centre point

[Dreadlegions]

I'm currently puzzling over reforms. What exactly is the centre point of the unit?

Is it the very centre, that has to stay the same no matter what?

Ie. can a unit of 5 knights never change formation, because the centre point would move?

Or is it measured differently?

[Calisson]

Reform: BRB p.14.
There are two constraints:
- the centre of the unit must be kept the same
- no model may move more than 2M as a result (see top of p.14).

The centre is not defined in the BRB, so you need to take the common understanding for "centre":
If you had a plank with the very same shape as your unit, you could hold that plank in equilibrium on one finger, provided that the finger was in the centre.
You just need to estimate where is that centre approximately, and have your opponent agree.
The new formation, whatever it is, needs only to have the same centre.
Note that you can rotate the orientation at will around this centre.
Note also that if the new formation has less ranks than the old one, the front line will have moved backwards.

Anyway, there's no reason why a unit of 5 knights could not reform. For instance, if you reform them from 5x1 into 3+2, all knights will have moved, which is fine.
Hope it clarifies.

-=-=-
EDIT
If you have trouble with the combat reform, please note the FAQ, which cancels the centre restriction:
Page 55 – Combat Reform, Reforming From Victory.
Change the first sentence of the second paragraph to “A
combat reform is essentially a standard reform (page 14), save
for the fact that the centre point of the reformed unit does not
have to stay in the same place.”

[Dreadlegions]

I'm ok with combat reforms, it's the centre point I'm struggling to grasp.

If it means the centre of the unit, ie. the middle, then it drastically reduces what reforms you can do.

If it simply means the centre of the front rank, a lot more reforms are allowed (but why does it not just say centre of the front rank?)

[Dreadlegions]

And what stops a unit of 5 knights from reforming 16 inches to the left of their starting position?

Seems a handy way of getting round the sideways movement rule...

[Calisson]

It is NOT the centre of the front rank.
It is the centre of the unit, as I described.

I don't see how in the world you could feel constrained.
You are allowed pretty much any new legal formation, facing any direction.
The only two constrains are that
- the new "middle" must be located at the same position than the old "middle",
- and no model should move more than 2M by doing so (this limitation is to avoid a goblin horde to reform to a conga line and deliver their fanatics).

Remember, the centre of the unit is a point, not linked to a model.
Examples:
In a 5x5 formation, the centre is the middle of the central model.
In a 4x4 formation, the centre is in the common corner of the 4 central models.

You can perfectly reform a cavalry unit from 5 x 1 (the centre is in the middle of the middle model) to become 3+2 (the centre being somewhere close to the rear of the middle horse).

You can reform a 10x4 horde into a 5x8 bus. In that case, the front of the unit will extend further than the old front, and the rear will extend further than the old rear.

And what stops a unit of 5 knights from reforming 16 inches to the left of their starting position?

Easy: the new centre must be located in the same position as the old centre.
What you say cannot happen.

[Red...]

And what stops a unit of 5 knights from reforming 16 inches to the left of their starting position?

A crowd of onlookers wielding pitch forks and torches, screaming "burn the rules munchkin!"

That and what Calisson said