Software defines (or will defines) a company - what it can do, how it does it, how it reacts. If you cannot read the code you don't know what the company does. If you don't write the code, you cannot define the company.
Defining the activities of an organisation is management. All the people called managers are at best coaches, giving a towel and water in the corner.
And so productivity is measured by organisation chnage - otherwise you are trying to measure typing speed.
(this is not to say we do not want to look at the tools we use to produce software, but this should be focused on CI-like throughput (ie Speed vs stability) not "correctness"