Your portfolio value is based on wholesale buyback (bid) spot prices at close of business Sydney time each day.
The portfolio value takes your total metal holdings and multiplies it by the “spot BID price” at the time. There is always a difference in the Bid and the Ask in the spot price at any given time and the Bid Spot price is not listed on the website, only the Ask price is.
So for accounting purposes you can use your portfolio value, but for your actual liquidation value you will need to see the ‘buyback price’ which is listed on the charts and prices page of the website.
Note that the value is an approximate value only – the actual value if you go to sell your metal will be different depending on the current buyback prices for the specific products you have.