Easy way to derive high level estimates for IT project

Are you stuck every time with a demand from your Manager to provide HLL(High Level Estimates) of a requirement within a limited time frame?Yes.

An easy way to derive/calculate high level estimates for a given development task lies in the historical data sheet.
This "Historical Data Sheet" can be maintained to store WBS(Work Breakdown Structure) of every estimates for all type(small/medium/large) task that has been executed till date on the given project.

This would help both new as well as old resources to grasp an idea about required development scope in terms of files/classes/LOC(Line Of Code) on a higher level.

Example:
On Apr-2009, I have received a business requirement that add an extra field1 to a webpage, I have given the WBS like
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i) Changes in XYZ JSP Page
ii) Changes in ABC component class
iii) Changes in LMN EJB class

Total 1 JSP and 2 Class

HLL Effort: 24 hrs
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Store this information in "Historical Data Sheet" with appropriate column and upload to shared location and communicate to all team members(Others will do the same).

Next time I got a similar requirement to add another filed2 after 1 year in Apr-2010, now there is 2 approach to provide a HLL, either you again drive inside a code to identify what all changes are there, else you simply refer the "Historical Data Sheet" to have and provide a "quick" HLL for the given task. You could add 10% margin to this accommodate the extra scopes.Thats it.

This could also be termed as "Re-usability" of one person knowledge about a product/area with other team members (At least for estimation).