All the Zetagi matchers actually utilise a 'Pi tank' or 'Pi Network' configuration.
That is - First variable capacitor, (Tune), from radio input to ground - across an inductor to the next variable capacitor, 'Load' which is connected between ground and the antenna connector.
It's just like the 'tank' final on many an old valve transmitter that would've been labeled 'Plate' and 'Load'. (See link below for configuration and mention of 'Dipping the Final')
Best just to look at the first diagram on that link than absorb yourself in the underlying maths.
Another good link to look at is here :-
Ah, that's better, far less maths.
The reason for this layout is so that the variable capacitor controls are wired such that they are grounded. That way they don't suffer the effects of 'hand capacitance' whenever you go to tune them or require extensive, (and added expense), methods of isolating the capacitors from the chassis and front controls.
The reason for one coil or inductor is that they were designed for CB use and not atypical Amateur band HF useage. Why pay for a switched inductor and associated switch gear when you're only using it on one band?
You can tune them as has been previously suggested but it can all become a bit of a pain in the ass chasing your SWR all over the place whilst constantly adjusting your calibration or 'Set'. Indeed, a dual meter setup can be a bit easier in that you aren't flicking your 'FWD/REV' switch constantly back and forth but you'll still be chasing that SWR.
The simplest way to tune them is to just 'listen'.....
Find a frequency that you're interested in but without an ongoing transmission.
Ensure your squelch is off and select a sideband mode popping up the volume to listen to that lovely cosmic background radiation 'shhhhh'.
Adjust the 'Tune' control until the loudest 'shhhh' is heard, you may have to turn back and forth to find the centre.
Then move onto the 'Load' control and do the same, back and forth until the loudest 'shhhh' is heard.
You're now pretty much bang on where you want to be and can now 'CAL/SET' your SWR meter for an accurate reading.
Then you can 'twiddle' gently a little further, 'tune' first then 'load' whilst reading the SWR meter and often get that elusive 1:1 SWR!
That'll be the settings for that particular frequency, on that particular radio, with your particular antenna.
Change any of them and you have to retune but you'll usually be just changing frequency not your radio and antenna!
You'll soon find the 'sweet spot' settings for any of the frequencies and take note of where the controls are set.
As the variable capacitors normally adjust across a 180 degree of motion I use the simple 9 o'clock to 3 o'clock analogy.
What a pain hey?
Just remember that they are an 'impedance matching device' or Antenna Matching Unit not a 'tuner', they match your radios impedance to the antennas impedance. Now you can see why they don't have simple 'frequency' markings and some don't have markings at all! (That's where the 9 o'clock, 3 o'clock thing comes in handy.
) The settings will be completely different for everyone depending on their impedances of their particular setup.
Now, getting onto your 'Lo, Lo-Lo' etc. tuning woes......
You've got a 'Pi - tank' on your radios Finals, matching your radio output to 50 ohm and also acting as a low pass filter.
You have your Zetagi matcher in line which is also a 'Pi - tank'.
You have an End Fed Half Wave antenna, this bugger will have a typical L-C-L base loading coil with a tap capacitor.
.....you may find it difficult to tune.
By all means, give it a go, you may strike lucky but you might have problems with it not reaching that far.
If that's the case you can simply switch another capacitor in line with the Zetagi matchers first variable capacitor running it in parallel, (remembering capacitance adds when in parallel). A switch squeezed in, placing a good Silver Mica capacitor between the rig side input and ground would do the job. Switch that capacitor in for lower frequencies and switch it out for higher.
You could 'squeeze' the inductor coil between the capacitors to raise it's inductance therefore lowering the frequency but you'll lose the higher frequencies. A longer coil with a switch arrangement to short out the extra length for high/low would also work but requires much more fiddling. But I wouldn't worry.....
...the big problem will be the base loading coil in your half wave antenna, it's a LCL 'T' match to tame the end fed impedance. If you 'clip' out that capacitor your Zetagi Matcher will take over the job of matching. Again, extensive surgery of your antenna and ruining it for anything else except your setup but will allow you to tune those lower frequencies.
In depth I know, but hopefully explains it all a little for you.
The much maligned and misunderstood, but in fact simple piece of equipment any radio operator can have.
So good I built my own, (a Pi - tank no less but with switched inductance), and it may not have 'pretty lights' or do anything automatically but I wouldn't be without it.
All the best,