Slitherine

In page 48 under "Units allowed to Fire" it says :
"In order to fire, a unit must fulfil the following requirements:
* It must ne an Infantry, an Artillery unit or an Artillery attachment"

Suppose that we have a large cavalry unit with an artillery attachment in one end,
Do I measure Firing Ranges and Arc of Fire from the artillery attachment base or from the unit's front edge in general?
i.e. do we consider that the artillery attachment is located at its exact position or do we imply that it is somewere in the regiment (regardless of the model's position) and thus the whole cavalry unit has the ability to shoot.

You measure it from the units frontage (or half-frontage if it is in extended line) - Just as you would an infantry unit.