1,67
Perhaps it is simple mathematic rule in order to get 60% out of 100% you must multiply the L50(Landing Distance) by 1,67 in order to get the Landing Field Lenght.
You can try and check let's suppose a plane lands in 1800 metres having 1800X1,67=3006 so Landing Distance 1800m Landing Field Lenght 3000
now if you make the 60% of 3000 it comes exactly 1800.
When a pilot have to check the maximum landin weight has to go back fron the available runway , take the 60% and find at wich weight a plane will have a landing distance long that amount.
that will be the maximum landin weight limited by the runway lenght that have to be compared by the landing climb limited weight and the structural weight , the lowest will be the Maximum Landing Weight MLW.
cuvcap