A million years ago, White's devised the perfect all purpose detector. Called the Coinmaster, it came in all kinds of flavors. The top of the line model was the 5900 and 6000. The 5900 was essentially the same as the 6000 with manual ground balance, rather than the auto GB of the 6000.
The blue box models use 4 'C' cell batteries and the handle is a backwards mounted bicycle grip. They are called Coinmaster 6000 Di Pro, CM 6000 Di Pro Series 2 and Series 3.
In the '90s, the Coinmaster got an update in the form of a new type circuit board, black paint, carbon lower rods, new coils, a new handle system that incorporated an armcup, and other changes. These were called the CM 6000 Di Pro SL and CM 5900 Di Pro SL. The SL stands for Slim Line. Why, I don't know, since it still uses the 4 'C' cells and is the same size as the earlier blue boxes.
You'll sometimes see an additional 'CB' designation, which designates a new circuit board design.
Around 1996 or so, the 6000 again got upgraded. It got a new lighter box. Updated electronics allowed the unit to run on 8 'AA' batteries. The 5900 was dropped completely from the lineup. Designations were -- CM 6000 Pro XL, CM 6000 XL Pro, and XL Pro. All are electronically identical, though the XL Pro represents the very last version manufactured, which means it utilizes the newest coil technology available at the time.
