It looks to me like you wind/unwind the antenna to the coloured markers to set the element lengths. It’s just a case of selecting the right lengths to get to resonance on the desired band.
Can you borrow an antenna analyser? The MFJ-259B is ideal for this work. Set up the antenna wound to the band markers and measure how well matched it is? You may find just a few turns more or less are needed to get to the best match. Then take it down and repeat to make sure the setup is repeatable. See what the 817 says when the analyse says best match too. You can then learn how to interpret the 817 display better.
I only use a 5m pole and have managed some 12500 QSOs for SOTA on HF using dipoles, 1/4GP and simple vertical (up and outs). Victor GI4ONL tends to use mainly a 4m pole and has logged 10500 QSOs for SOTA on HF. The longer the pole the better but short, compact and light poles do work well IF the antenna is correctly setup.