Combination A-Scan/Pachymeter with graphic display and IOL power calculation software. All A-scans and A-Scan/Pachymeter combination units include firmware module with SRKII, SRKT, Holladay Dioptimum and Binkhorst II formulas. Audible tones increase in frequency the closer you get to visual axis. Constant tone when alignment is achieved with corneal indentation. Triple tone when measurement is obtained without corneal indentation. All Model DGH 5000e and DGH 5100e are equipped with corneal compression detection software, and are upgradeable to the water immersion option.