The 0.68 * height that MB reports for Nordic walking seems about right
for me. At 1.80m, I found by experiment that a 120 cm (67% of height)
pole length on my Black Diamond treking poles is feels good for power
walking. My off-trail classic skiing poles are set to 145 cm (80% of
height), my track classic poles are 150 cm (83%), my skating poles are
cut to 162.5 cm (90%), down from skating with 165 cm poles (92%).

One of the advantages of using the adjustable BD treking poles (besides
being able to collapse the 3-section poles) is trying out the different
lengths. I started walking with the treking poles at my backcountry
length and adjusted down the the 2/3 height by feel. I can also
lengthen them back to 80% of height for up hill bounding.

Edgar