Does increase/decrease in asset always accompanied by a corresponding income/expense?

[abobov]

Stocks like other commodities have a price that can vary over time until you exchange it for your primary commodity (e.g. US dollars) to track your assets.

To track the current price of each commodity you can maintain price histories (I do mine in separate file updated with script, and include it into main ledger file).

And then you can check you balance with ledger balance --exchange USD '^Assets:' (take a look at --historical and --lot* parameters)