May I ask why you're doing this? 
There's a math puzzle factor to this and maybe a flip a coin aspect too. But over the last 3-4 months difficulty changes have been sort of unpredictable - there was even a decrease if I remember correctly.
All due to a looong list of factors that affect the total network hashrate, including the less obvious ones like homemade rig uptime lapses, to FPGAs being sent back to BFL, people going on holidays and just not caring, to individual miners switching to other pools, to solo, to other cryptocurrencies ....
Don't get me wrong I'm tracking things too but why such a real time approach?
There's a math puzzle factor to this and maybe a flip a coin aspect too. But over the last 3-4 months difficulty changes have been sort of unpredictable - there was even a decrease if I remember correctly.
All due to a looong list of factors that affect the total network hashrate, including the less obvious ones like homemade rig uptime lapses, to FPGAs being sent back to BFL, people going on holidays and just not caring, to individual miners switching to other pools, to solo, to other cryptocurrencies ....
Don't get me wrong I'm tracking things too but why such a real time approach?