In 1934, AO introduced No. 589, the Additive Effective Power Phoroptor, once again enlarged and improved. The lenses were increased to ¾ inch diameter, the permanent size, and the unit was much more massive, with a weight of 7 lb. 9 oz., and with a range of +16.87 to -19.12 and -6.00 cylinder, with auxiliary lenses to increase these to +18.87/-21.12/-8.00. All these models resembled the original DeZeng model in design, but No. 590 of 1948 was a completely re-designed device, much larger and heavier, and more modern. It weighed 10 lbs. 7 oz. This was followed by another complete re-design in 1956, the RxMaster, which became the prototype of all modern phoropters, and was updated to the Ultramatic RxMaster in 1967, which is the current model.