This is calculated after-the-fact. The final effective exchange rate that I got is based on initial starting cash, and then on subsequent transactions made against my bank account and credit card.

All dollars are Australian.

 * KVB Kunlun, before the trip
  * $1995.05 -> 170,000 yen
  * 85.211 JPY/AUD

 * ATM withdrawal on 2012-03-07
  * $490.22 -> 40,000 yen (AUD value includes a $19.13 bank fee for the withdrawal)
  * 81.596 JPY/AUD

 * ATM withdrawal on 2012-03-10
  * $481.80 -> 40,000 yen (AUD value includes a $18.89 bank fee for the withdrawal)
  * 83.022 JPY/AUD

 * ATM withdrawal on 2012-03-11
  * $243.40 -> 20,000 yen (AUD value includes a $11.94 bank fee for the withdrawal)
  * 82.169 JPY/AUD

 * JR East shinkansen ticket on 2012-03-09
  * $61.70 -> 5,240 yen ticket value (AUD value does not include bank fees, not yet confirmed)
  * 84.927 JPY/AUD
   * As an estimate, $64.00 would make it 81.875 AUD/JPY

Now calculate the weighted average. I'll just be lazy and do `Sum(all JPY values) / Sum(all AUD values)`

{{{
    170,000 + 40,000 + 40,000 + 20,000            270,000
------------------------------------------  ==  --------------  ==  82.514
1995.05 + 490.22 + 481.80 + 243.40 + 61.70          3,272.17


For reference, increasing the denominator by a few AUD, to 3275, reduces the exchange rate to 82.443
}}}