Peak to Peak

Double Amplitude means peak to peak amplitude.

e.g. 1.25 mm peak amplitude means 2.5 mm double or peak to peak amplitude.

A standard relation employs peak amplitude :

acceleration(in 'g') = 4*pi*pi*f*f*d / 9810 where d is in mm and peak amplitude

e.g. f = 44.56 Hz and d = 1.25 mm peak gives acc = 10g

Regards

Deepak