It's been a tough week for Warren Buffett's big investment in IBM.
Big Blue's stock plunged 8.3 percent Friday to $190 per share after the company reported disappointing first quarter revenues.
Assuming Berkshire's stake is still around that size, Friday's slide cut the value of those shares by $1.168 billion to $12.94 billion.
That's on paper, of course. Berkshire won't actually lose any real money until it sells the shares, and given Buffett's buy-and-hold track record that won't happen until years from now, if it happens at all.
Still, it's a big number and it represents roughly half of Berkshire's paper profits on the stock it started buying in 2011.