``Manual segmentation refers to the process whereby an expert transcriber segments and labels a speech file by hand, referring only to the spectrogram and/or waveform. [...] The manual method is believed to be more accurate. Also, the use of a human transcriber ensures that the segment boundaries and labels (at least at the narrow phonetic level) are perceptually valid. However, there is a need for explicit segmentation criteria to ensure both inter- and intra-transcriber consistency, together with (ideally) some form of checking procedure. Sets of guidelines for manual segmentation have been developed by various projects. One such is Hieronymus et al. (1990), which uses the four levels of underlying phonemic, broad phonetic, narrow phonetic and acoustic. It also retains the same base phonemic symbol even at the acoustic level, to facilitate the automatic determination of boundaries at the phonetic level once the boundaries at the acoustic level have been determined. One should not expect more than 90% agreement between experts.'' (From , p. 152.)The basic principles that were listed in section apply also for the manual segmentation and labeling. You should focus on a consistent training of the segmenters and labelers to maximize inter-labeler agreement (see also section .