What is the best method to calculate the correct productivity / man ?

by giving them sense of responsability ,you can set the machine or labor production efficiency but the complex jobs varis the productivity .

for example if a technician have to plug the IC on pcb  he can change100s of it but to find fault in an ic can take (may be )3 days.

so the efficiency can be caculated in production but it varies in maintenance.

A good and fair record keeping system/programme, make sure it110% accurate and test it yourself before any flaws come out in the end, I had it once where the IT guys did the set up incorrectly and was making money, but it was recorded for another dept.

LET HIM WORK INDEPENDENTLY

The correct productivity should includes all costs in the production process starting from row materials cost, operation cost, storage cost & all other supplies like salaries, spare parts, maintenance costs. In other words it is all costs on the factory from door of the row material entry till the door of finish product shipping. All this costs should be divided by employees to get the perfect productivity calculation

By deviding his/her production by the time spent to produce it.

Productivity is a measure of how much pproductive (useful) outcome is obtained from a person, a group, a team, a department, a function, or an entire organization compared to the supplied input into the process(es) associated with producing this outcome  ..... (MY OWN DEFINITION) 

So, it really depends on several factors before you can reach at the correct, suitable, indicative, useful definition of productivity.  I can possibly devise such a measurement system for productivity ( as in the case of KPI's/KRI's for a balanced scorecard project) that refltects the organization's actual need on case by case basis 

Another thing, there is an overlap/confusion between "productivity" and "profitability" that results in bad and misleading consequences and conclusions.  

1. Productivity is related tp products and production (act of producing)  
2. Profitability is related to selling the products (from1 above) and making a profit from it 

So, in conclusion, if you are about making a performance measurement system to assess/improve corporate performance, be careful to select the right parameters and use them correctly to get things better and not worse !!