Pier to Pub Swimming Training

I am participating in the 2010 Pier to Pub at Lorne on January 9, 2010. It is a 1.2 km open water course. I heard that the rule of thumb is that for every 1km of open water swimming is the equivalent of 2kms in the swimming pool. Thus my target is 2.4km in a swimming pool (48 laps of a 50m Olympic sized pool). My progress via Google spreadsheets (which is automatically updated) is below:

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