Dan describes how he developed Northfield Financial Services as making the evaluation of many possible asset portfolios affordable.  Instead of having to buy expensive software that could only be run on expensive mainframe computers, Dan's innovation made it possible to assess portfolios in sophisticated ways using personal computers.  He explains the services for various groups of clients that Northfield provides.  In the process, Dan tells how his modeling contributed to finding the fraud perpetrated by Bernie Madoff.  Dan reveals how tennis played a role in his early career and his interest in Court tennis or "real" tennis as practiced in medieval times.