customize instrument tuning

[BB]

Im trying to understand the the tuning parameters. I worked with a couple of years ago, but cannot remember. The example in the manual uses

    
%Cuatro Venezolano    a - d' - f'# - b
cuatroTuning = #`(,(ly:make-pitch 0 6 0)
                  ,(ly:make-pitch 1 3 SHARP)
          ,(ly:make-pitch 1 0 0)
          ,(ly:make-pitch 0 5 0))

As far as I remeber and I found in my old code I used another syntax?

cuatroTuning = #'(11 18 14 9)
But I cannot remember the meaning of the numbers either.

 

How can I define an Instrument in major thirds tuning?
i. e. M3Tuning = c as c e as c

Regards

(By the way, there is another Cuatro in use: Cuatro Puertorriqueno     5x2  strings   Bb - ee' - aa - d'd' - g'g')