Last thing - ‘Sunday morning voluble’ here 
Using a ‘pillar’ numbering system is really useful in open spaces like factories or production units where machines may stand isolated from walls.
Looking from the ‘front’ of the building (arbitrary side that is chosen as the datum) AA BB CC DD from left to right, 11 22 33 44 from front to back.
You don’t need to have actual, physical pillars - you can use roof joist junctions, for example.
It can be used for everything from operator/tech to electrical, HVAC, warehouse, materials storage, etc., although with 20 machines you can probably get away with anything that works.