The post-World War II Dictaphones recorded by cutting grooves in a plastic “Dictabelt”, which could be flattened and sent through the mail in a regular envelope. Because the mechanical recording was considered too difficult to alter, testimony recorded on a Dictabelt was, unlike magnetic recordings, admissible in court in many jurisdictions. In the late 1970s, faced with competition from IBM dictation machines that recorded on a magnetic belt and allowed backspacing to correct errors, the company introduced magnetic recording machines, initially using the regular Philips Compact Cassette, and later smaller cassettes suited for portable machines.