The paper gives sufficient conditions to have the equality between two diametral dimensions of metrizable locally convex spaces and examples of Köthe echelon spaces satisfying them. It also provides examples for which the equality does not hold.
"On the equality between two diametral dimensions." Funct. Approx. Comment. Math. 56 (1) 95 - 107, March 2017. https://doi.org/10.7169/facm/1594