How to get consistent sample frequency from Matlab mobile app?

Hi all, I am using Matlab mobile app to collect accelerometer and gyro data. I am using m.Logging=1; pause(0.1); m.Logging=0; to collect data, Every time I run this section in a loop I get different array size. I am trying to learn FFT and need consistent sample frequency. I might be doing same mistake, will appreciate any help.

Thanks for your time,

Krishna