Resume writing tips?

I am currently updating my resume. I've run into a slight problem - many of the companies that I've worked for I started off at entry level and moved my way up to a higher position. Should I list these as two completely different entries, or combine them? My resume (for the same company) currently looks... show more I am currently updating my resume. I've run into a slight problem - many of the companies that I've worked for I started off at entry level and moved my way up to a higher position. Should I list these as two completely different entries, or combine them?

My resume (for the same company) currently looks like the following:

January 2005 - May 2007 Clerk
May 2007 - Present Supervisor

Or should I do it like this:
January 2005 - May 2007: initial position Clerk, promoted to Supervisor
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