They are not interchangeable in a scientific setting...and the professor is an ass - never liked him. ;)
English is a stupid language. Take skim and scan. People use them interchangeably, but scan can mean the exact opposite of skim.
scan /sk=E6n/ verb,scanned, scan=B7ning, noun =96verb (used with object)
- to glance at or over or read hastily: to scan a page.
- to examine the particulars or points of minutely; scrutinize.