37% is today's Daily Digit in Europe - that's how much shares in Invensys have jumped since it agreed to sell its rail business.
Siemens is buying it for a hefty $2.8 billion.
That's not much less than the value of the entire Invensys operation, which includes chemicals, power and mining businesses
Pierre Briancon from Reuters Breakingviews' says the deal caught almost everyone by surprise.
SOUNDBITE: Reuters Breakingviews European Editor, Pierre Briançon, saying (English):
"They may be able to pull off synergies that were unsuspected under the deal. This is a company that has a few problems of its own, so expansion is part of the answer, definitely. They should maybe look domestically at where the future lays. There are big unknowns about some of the industries they were in -- nuclear to mention one."
Siemens says it's been eyeing Invensys Rail for a decade.
The German engineering giant is trying to save almost $8 billion by focusing on its core businesses.
It's also trying to close a gap with rivals such as ABB and General Electric.
But at current estimated profit rates it could take 15 years for Siemens to break even on the deal.
Some are wondering whether they might regret their decision further down the line.
Daily Digit: Invensys shares jump on rail deal (1:26)
Nov. 29 - Invensys shares jump by 37% in two days after Siemens said it was paying £1.74 bln for its railway signalling company. Joel Flynn reports. ( Transcript )