Hook the Amplitrex to your laptop and it will trace the tube. I have never bothered to use mine in that mode. I like that it gives you real measurements, plus the expected values, and for ultra idiots like myself, it provides the "good," "weak," etc. evaluation.
The thing with estimating remaining life is that it really depends on how a tube is being operated. If operated gently, it may last a long time after beginning to test weak. Also, a weak tube may still be able to do its job extremely well depending on the circuit. I had a pair of 6sn7 tubes that tested quite weak on the Amplitrex, but the amp sounded good. I emailed Audio Note (the maker of the amplifier) about whether it was safe to continue using the "weak" tube and I was told to continue using it because, in their circuit, even a weak testing tube could sound just fine.