Settlement price
The stock price information provided by StockWeather.com,Inc. uses settlement price as previous day's closing price. Settlement price is the data, delivered from Tokyo Stock Exchange as reference price of the price range on the day.
Settlement price is basically same value as previous day's closing price. However, on the date of ex-rights, such as splits, merge, dividends, and rights offering, the amount of rights is adjusted from previous day's closing price.
e.g. 1 - Case of ex-stock split
Previous closing price: JPY 1,000
Stock split: 2-for-1
Settlement price: JPY 500

If next day's stock price is JPY 550, the net change and change ratio of previous day will be calculated as follows.

Net change: JPY 550 (Current price) - JPY 500 (Settlement price) = +JPY 50
Change ratio: (JPY 550 (Current price) - JPY 500 (Settlement price)) / JPY 500 (Settlement price) * 100 = +10%
e.g. 2 - Case of ex-dividend
Previous closing price: JPY 1,000 (with Rights)
Dividend: JPY 10
Settlement price: JPY 990

If next day's stock price is JPY 1,010, the net change and change ratio of previous day will be calculated as follows.

Net change: JPY 1,010 (Current price) - JPY 990 (Settlement price) = +JPY 20
Change ratio: (JPY 1,010 (Current price) - JPY 990 (Settlement price)) / JPY 990 (Settlement price) * 100 = +2.02%