What is the delta parameter in $\tt scal2freq$?
The delta argument in the scal2freq MATLAB function is the sampling period that relates to the data sampling frequency (i.e. delta = 1/Fs).  A good description of this function can be found here: http://au.mathworks.com/help/wavelet/ref/scal2frq.html it also includes an example including how to calculate and define the delta argument.  I hope this helps!