A good example of an ideal scenario would be the Dodge Book for construction cost estimation. Any possible job related to constructing a building in the book, with hours and materials, with variations for high-end and low-end design and materials. From there, you can scale your effort accordingly, i.e., if you build a shower stall that's 1.6 times the typical, you can scale the effort for the new job. So if you know that a defined DSP-based circuit board cost 600 hours to design and lay out, a board with 50% more complexity will cost correspondingly more. One beauty of this is that the customer cannot attack your cost basis, they can only downscope. Sadly, my previous company seemed to be institutionally incapable of estimating that way, and the customer's buyers would attack our cost estimates and we'd wind up knuckling under.
Somewhere else, there was mention of lump work packages. That's OK, but bear in mind that costs change, sometimes abruptly, so even though the package is disassociated from the hours, ultimately, you're still accountable for lump_sum/hourly_cost. We've often been caught flatfooted when "someone" determines that the wrap rate is 20% higher, so you suddenly lose 20% of your budgeted hours, or dollars, machts nichts. It's particularly bad if it's retroactive and you've already spent a big chunk of your budget and carefully managed the cost to the original estimates. Suddenly, you've gotten 20% taken off the top, but it's more like 40% cut of your remaining budget, since you've already spent 50%.
Obviously, the ideal approach is to have a management reserve, but in a tall contract structure, i.e., one where Boeing subs to Raytheon who subs to someone else, everyone along the chain is holding a reserve, except the guy on the bottom, who started out slim, and is working to an even slimmer budget, because everyone above him has taken a reserve cut.
Even so, given a lump amount, you still want to be managing and statusing to smaller work packages and assignments, to ensure that ME Joe didn't wind up frittering away 500 hours on an FEA that wasn't even that critical, and should have only spent 80 hrs.
The biggest impediment to best practice is simply the common practice of underbidding. What I've observed, over the years, is that the initial bottoms-up bid, fromt the actual executors of the work is often correct from the get-go, and the management "challenges" and "trims" simply put you deeper in the hole each time they thumb the cost volume and decide it's still not a winning price.
Unfortunately, it's so institutionalized that most experienced customers build the underbidding into their own cost estimates; only inexperienced customers who buy into our rosy predictions of cost get screwed, and fired off their own programs when we overrun.
TTFN
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