The Sabba scale is a heptatonic scale that can be built using the following steps between notes: ¾, ¾, ½, 1½, ½, 1, 1.
If we use (b/2) to denote a quarter note flat (a drop by a quarter tone), then one example of the Sabba scale would be A, B(b/2), C, Db, E, F, G. This example is shown below in traditional notation (the horizontal line through b denotes a drop by a quarter note) and in guitar tablature notation (to the extent that guitar tablature allows quarter notes).
This is an Arabic scale that uses quarter tone intervals. This scale is not close to any commonly used semitone heptatonic scales, but one way to obtain this scale is to and to take the sixth mode of the Spanish gypsy scale, raise the first degree of the scale by a semitone and the second degree by a quarter tone. The Spanish gypsy scale corresponding to the example above is C, Db, E, F, G, Ab, Bb. The sixth mode of that scale is Ab, Bb, C, Db, E, F, G. Raising the Ab to A and the Bb to B(b/2) gives us the Sabba scale above.
Scale, Scale (index)