Close Order - How close is 'Close?'

Close Order is the distance soldiers are to take in anticipation of engaging the enemy.  The intent of Close Order is to present a united front upon which the enemy shall break as a wave on a rock.
 

There are, however, different interpretations for how close is 'Close Order' between files.

46 centimeters/18 inches from one soldier to his mate on either side The Tactiks of Aelian, 1616, John Bingham (who uses cubits for measuring and refers to Close Order as 'Shutting.'  Like Barriffe, Bingham is specific as from where to start the measurement: the center of the soldier) The A.B.C. of Armes," 1616, 'J. T. Gent' (most likely a Gentleman with the initials J. T.) Souldiers Accidence, 1635, 2nd edition corrected and edited by G. Markham The Principles of the Art Militarie, 1637, Henry Hexham (who says Close Order is for pike only) For these sources and counsel, Patrick Gaul of the Renaissance Military Society has been most helpful.

Shoulder to Shoulder Directions for Musters, 1638, author unknown (for pike only to make or receive a charge)   Sergeant Subtlelus says: Regardless of how one construes Close in Close Order, that construal may be utilized only when all in a unit are informed of it and will abide by it.  Accord is best established at the first assembly before any drill commences.

It may be argued that while musketeers should have sufficient room to handle their weapons and thus shoulder to shoulder is too close, it may be advantageous to have pikemen bunched that tightly - or tighter - for push of pike.  For such, there is Closest Order.