It's right up Tesla boss Elon Musk Ali is a wink tow, anti establishment types who love the idea of a digital currency that's beyond the reach of any government.

The news pushed up the value of Bitcoin to a new record now approaching $50 and it further boosted the market capitalization of Tesla, which is already at more than $800 billion worth more than the next 10 or so car manufacturers combined.

It raises a geeky but important question to today's accounting rules.

Mean Musk's company won't mark up this week's game or any subsequent uplift in the value of its Bitcoin holdings.

The reported value on testers books can only go down.

That's because the only place Cryptocurrencies fit into accounting at the moment is as what's called intangible assets.

That's usually a category for squishy things like brands and trademarks, and the rules only allow them to be written down in value, never up.

But Bitcoin is a bit like virtual cash or a non government currency.

If you don't like those analogies, it's akin to a speculative investment.

Some see it as a kind of hedge against inflation, a digital version of gold.

But the accounting doesn't get close to matching any of those things.

Corporate reports could become seriously misleading if crypto investments by companies catch on, the accounting will need a rethink.