scientists, creators Cheryl Heuton and Nick Falacci created a show with one as the protagonist. Inspiration for Charlie came specifically from Richard Feynman. Finding the actor who would portray Charlie would be a challenge. Over one hundred actors auditioned for the role of Charlie Eppes. One of the actors was David Krumholtz, who later admitted in an interview with TVGuide.com and in an interview with USA Weekend's Lorrie Lynch to failing math in high school. Krumholtz was cast as Charlie because of his ability to make math sound natural. To prepare for his role of Charlie Eppes, Krumholtz spent some time at Caltech talking to professors and walking the Caltech campus, attempting to understand both the basics of the math and the mathematician's mind. He even spoke with Dr. Tony Chan of UCLA about mathematicians’ work while filming the first pilot. Math consultants helped Krumholtz understand the basics of the equations on the show. Early on, Professor Rick Wilson's graduate student, David Grynkiewicz, showed Krumholtz how to write his own equations and even filled in for his hand in several episodes. Krumholtz now frequently writes the equations himself. Krumholtz memorizes the pages of mathematical equations and concepts that are a part of the script.<ref>{{cite web |url=http://www.thefreelibrary.com/DIVIDE+AND+CONQUER+CBS'+%60%60NUMB3RS+ADDS+A+NEW+TWIST+TO+THE...-a0127888051 |title=Divide and Conquer CBS' Numb3rs Adds a New Twist to the Crime-Show Formula |access-date=September 9, 2009 |author=Valerie Kuklenski |date=January 27, 2005 |publisher=The Free Library |work=Los Angeles Daily News}}</ref> When doing scenes involving audience-visions, Krumholtz prefers to recite his lines as the cameras are rolling; producers went along with this because they reasoned that if the cameras weren't rolling, the lines wouldn't make it into the show. (Audience visions are Charlie's visually-aided explanations of the mathematics involved in a case.) Reception Early reception of Charlie varied according to the audience in question. Due to television production's traditional approach of utilizing only two worlds for filming, production staff initially opposed the idea of Charlie being a college professor. Some even unsuccessfully suggested to Heuton and Falacci that Charlie should be working with the FBI full-time as an employee. When the pilot was previewed, the reception was more positive. CBS executive Nina Tassler liked Charlie. The focus group that watched the original pilot for Numb3rs loved him. When Numb3rs was previewed for the TV critics, the reception was different. Melanie McFarland, TV critic for the Seattle Post-Intelligencer, stated that Charlie was not original as of the Pilot.