Why does Google adwords tool shows different search volume

[seoug_2005]

I am not able to undertand the difference in search volume for same keyword under different heading. Let me make it clear. When i enter "Drupal Developement" in adwords tool, at the top, it shows

Search term (1)

Keyword                      Global monthly searches

drupal development                 390

Just below, it shows,

Keyword ideas (100)

Keyword                                       Global monthly searches

drupal development                       40,500

I have selected the location U.S.

My question is there is a huge difference in 390 and 40,500. Which is correct ?

[CPLDistribution]

No idea why you are getting this issue, however, I think 40500 is the correct figure for broad match. 390 seems far too small, just consider the number of people you would get searching for drupal development [city name].

I am based in the UK and the external keyword tool is delivering the following results:

Drupal development - broad, global - 40500

Interestingly though:

Drupal development - local, exact - 390

[KeriMorgret]

It does look like a broad vs exact match issue in numbers.