Jam Jam
Levers down, pick the key
Tune with all levers down. The Jam Jam preset covers 34 strings from C2 to A6 in C major; two other presets give the targets for a harp set up in E flat major or G major. Pick the one that matches how your instrument is strung and regulated.
From the bass up, one string at a time
Pluck each open string from the lowest to the highest. The tuner locks the nearest string and shows its target; turn the tuning key until the needle sits in the green band, ±5 cents. The bass strings are read a little slower than the trebles: pluck them clearly and wait for the needle to settle before turning.
Go round twice
Tension on a harp is shared across the whole frame. After a first pass, the first strings you tuned have moved a little. A second, quicker pass from the bass up fixes that. New strings will need a few extra passes over the first days.
Tune it now with the free online tuner: