They are just not standard... From 0-60 seconds in increments that are multiples of 5,
and in-between using non-standard 5/6 second increments e.g. from 10-15 seconds as follows:
10, 105/6, 112/3, 121/2, 131/3, 141/6, 15
I would consider non-standard seconds indicators a design decision and
considering the marks double as alarm indication, a very efficient design decision...
In my opinion... ; 
C