CBS Radio White House correspondent Mark Knoller doesn't shy away from Tweeting about the minutia of his job. Sometimes it's frustrating, but sometimes it can be a very good thing. Like today, when he gave an impromptu lecture on the history of presidential writing instruments. Here it is:

Only the signing page is on the table - not the 2300 page FinReg legislation. Obama uses about a dozen pens to sign his name.less than a minute ago via web

Bush/43 began his term using multiple pens, then abandoned the practice and used a single pen to sign his name to legislation.less than a minute ago via web

In the 70s, the press room wall contained a framed WH display of about 30 pens used by LBJ to sign "great society" bills into law.less than a minute ago via web

@douglaslucas Presidents use multiple pens to sign legislation to give memento to key members of Congress who got bill enacted.less than a minute ago via web

Sometimes presidents have to use more pens than they have letters in their name, so they dot I's and cross T's with different pens too.less than a minute ago via web

@RobMyers1968 Truth is, it really doesn't look like a signature when you sign your name using a different pen 1 letter at a time.less than a minute ago via web