Cry Me A River

I went to meet my supervisor just now and i'm screwed. He asked me to perform calculation on directional difficult index in short DDI.

Based on the journals we read and discuss just now, the formula for DDI will be as such:

DDI = log [MD x (AHD/TVD) x TOR]

Where:

MD = measured depth

AHD = along hole displacement

TVD = true vertical depth

TOR = tortuosity

But the question is, how to calculate tortuosity? Both of us have no idea of the formulae and he just asked me to google it or look up for in it SPE.

T_T My SV will be outstation to Perth for 3 weeks so i'm screweddddd... ... haih!