You bought it to complete the trilogy of equipment measuring: V vs t, V vs f, and now f vs t. (If you don'tn have the second, go and buy a spectrum analyser asap).
Yep, I do have a spectrum analyzer. Albeit it's a nice shiny new Rigol one, not one of those sweet beige/grey HPAK ones!
That said, I have been toying with buying a beige/grey HPAK dynamic signal analyzer as well.
Now you have the trilogy, you can start wondering why HPAK doesn't sell MDAs any more. That will get you wondering whether the modern generation of fast measuring frequency counters can do the same or a better job. That leads to looking at things like the Pendulum CNT90 (IIRC); ice-tea has one available, I believe. I'd buy one, but I'm overloaded for the foreseeable future.
TBH, even this antique probably exceeds my needs (and skill / knowledge) by a considerable margin. As far as "doing the job" I'm not really worried. At this point, this really is starting to become more of a "oooh, I need one of those to finish my collection" deals, more than a "I need this to accomplish goal X, Y or Z" deal.
That said, my frequency counter (excluding the ability to use a scope or spectrum analyzer to do that) is arguably not exactly of the "modern generation". See up-thread a few dozen pages or so... I just got a nice, "modern" HP 53132A a month or so ago. Still... with some upgrades, I think it's going to be quite nice in its own right.
BTW, the MDA is fun; You can also use it to measure sub-ns risetimes of digital signals.
Hmm.. interesting. I hadn't even thought about this much from a perspective of working with digital signals. Ah well, reading the manual (and old eevblog threads on these, which I've already looked up and skimmed over a bit) will be a lot of fun down the line. I don't think this thing is going to be something I'll use every day, but it may turn out to have more use than I expect.