A system and method for operating a mass flow controller is described. In particular it relates to an apparatus for determining the location of the apex of a dental root canal wherein the apparatus allows the acquisition of more accurate data in a shorter time span. The web screen obtaining section obtains information about a web screen by making a request to a web server. Once a block-wide encrypted buffer has been filled from an external memory source, the block may be decrypted using an encryption algorithm, the triple DES, etc. Thus, the set-top box can delete all of unnecessary program files in the hard disk recorder in a short time period.