Keeler Pulsair tonometer differences

Dave, hi again,

I would like to ask you another question about the tonometers. This time about the Keeler Pulsair non-contact series. There are different models, some of them are quite old, for example: Keeler Pulsair 2000, Keller Pulsair 3000, Keller Pulsair EasyEye. I am interested to understand the differences between those. It is natural to expect the later models to be more accurate. Is it true? And what about their compliance with the self-tonometry? Are there models which are not appropriate for self-tonometry, less-convenient, etc.?

Thank you in advance.