LAST Wednesday was a big day for the railway signalling community with the announcement that Invensys had agreed to sell its rail unit to Siemens for £1.7bn in cash. This might seem like an awful lot of money for a company that made a profit of £116m on revenues of £775m last year, but it is perhaps a fair reflection of both the capabilities of Invensys Rail and the breadth of its portfolio, which neatly complements Siemens own signalling business.