One of the original draws of the Zero 4 and zero 8 mixers was the inclusion of a Master global midi clock generator and control section built into the actual mixer.  I generally found it to be a very tidy solution for chaining and syncing multiple midi devices/instruments that needed to be kept in sync with a setup. 

The presence of the MIDI clock generator control section on the mixer is intuitively implemented through what would normally be used for auto BPM counter/BPM sync and adjustment dial for the mixers on board sampler and FX section whilst in analogue mode.  

In Ableton the MIDI clock generator and controls for the Z-4 mixer can be activated in the setup menu under the midi section. The lowest speed you can drop to using the mixers midi clock generator is 40BPM.

However the only draw back is that any changes in pitch/tempo/BPM using the global midi clock generator and control will not be recorded to a live set despite being able to make changes to them during a the course of live performance/set. The recording will essentially remain in its default start BPM count. 

The only way to get round it if you do want to record actual BPM changes within your set/performance is to just not use the mixers MIDI clock generator, and instead assign a midi control to the BPM adjustment controls within the Ableton app itself. 

I wanted to start recording BPM changes to my sets too which was the only reason I stopped using the mixers midi clock generator when putting together sets using the mixer. Even worse was the fact that when I did stop using the mixers midi clock generator in order to start recording BPM changes, it caused my machine to completely freak out like someone else was remotely using what I was doing via a stream, and the BPM changes that I was making and recording to my sets screwed up their setup and in turn screwed up mine. 

Initially there were symptoms of Ableton either completely crashing, audio completely cutting out for the set to continue recording as if nothing had happened (but without any audio), as well as constant audio drop outs and stutters. But after a year or so this isn't so much the case now.