From Off... single short click to enter high mode, then 6 double clicks (with the light changing between modes H1 and H2 with each double click) will enter you into the mode that rotates between the three H2 levels by additional double clicks: 140lm, 100lm and strobe. Once the right level is reached it can be memorised for the H2 mode by switching off the light with a single short click.
So for example I normally have H2 set on the 100lm mode: switching on the H51w in high gives me the H2 mode, then 6 double clicks gives me H1, H2, H1, H2, H1, H2, then another double click gives me H2 again (100lm) then another double click gives me 140lm mode, another double click gives me strobe.
Normally when selecting the high mode the light selects the last used used mode either H1 or H2, but if strobe mode is saved for H2 the light will start in H1 when high mode is chosen.
I think there may be a flowchart for the ZL UI floating around but it possibly have been for one of the handheld lights SC50/51??? Anyway the UI is the same as the H51.
