Copied and pasted from an email from TLC, below you can find the new 2012 formulae. TLC haven't published this info on their site as of now but no doubt will at some point - please use their information if there is a difference.
A key detail to remember is that the input "consumption" value needs to be the total uncontrolled units (kWh) used over a 92 day period, or at least an estimate of that based on readings taken from some appropriate period from 2011 (June through September for all but dairy farms which instead are analysed using the September through December period).
For a completely uncontrolled installation or meter that has no controllable load attached, use all of the recorded consumption. For "mixed meters" it seems TLC are still using 65% of the total units in the "southern areas" and 75% for Te Kuiti north. For the "Limited Off Peak meters" 55% of the actual consumption recorded is used. Night time consumption is also disregarded if metered separately.
All of these factors and adjustments as above can compound the inherent inaccuracies in the formulae as these percentages are just some kind of estimate that TLC has never properly explained or supported with detailed data.
These formulae clearly also come direct from a spreadsheet (e.g. Excel) so interpret them in that context (* is multiplication, / is division, ^ is exponentiation, IF is the "IF function", etc.)