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Design by rule of thumb

2010-12-15

I am collecting all "rules of thumb" examples in engineering used to either design or give a design a quick sanity check. Could you please e-mail any that you use or know of to me. If you know the origin or explanation (maths) behind it, I would appreaciate it.

I think it is very interesting and have to date not yet found a database of these "quick short cuts", which is the result of years of experince in engineering.

A rule of thumb given to me for evaluating another person's estimate was as follows. Divide 50 by the person's age. Multiple the results by the estimate. Example. estimate 5 weeks, age 35, 50/35 = 1.43. Plan for an effort of 5 x 1.43 = 7.1 weeks.(filter) You learn over time that stuff happens. Sick time, phone calls, a customer is down & needs help now....things than have nothing to do with the initial task but will take time from it.

After age 50 (this assumes you have been doing this type of job for a good portion of your working career) you know about these things & have baked this into the estimate with little thought. If a factor of less than one proves to be needed, the over 50 guy may not be accounting for productivity tools. Just a few years ago we waited a week to get photos from staff in the field. Now we can have photos in a few minutes & request more while the person is still on the site. This turns 1-2 weeks into 1 day effort. Same is true with CAD files vs mailing paper prints.


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