Measurements can be taken in centimetres or inches.  
Use a flexible measuring tape and have the tape sitting comfortably snug against the body. Not too tight and not saggy!
1) 'Neck':measure around the base of the neck at the widest, thickest part.
2) 'Neck Length': Only required for drying coats. Measure from the top of the neck to the base
3) Base of neck to base of Tail
4) 'Body Length': Middle of chest to in-line with base of tail
5) Ribs: Around the chest just behind the elbows
6) 'Waist': The thinnest part just in front of the hindlimbs
7)            Harness Clip Access: Measure from the base of the neck to where the access hole is required.