The horizontal (flat) part of the baseline activity that is used for the baseline start and end cycles in baseline settings. Manually, it is best determined in the log-view (as it amplifies the background activity changes). Some instruments use cycles 3 to 15 as default baseline range and some employs adaptive baseline adjustment (a unique setting for each well or tube). Most occurrences of unexpected amplification curve distortions (tilted baseline or irregular shapes) are due to incorrect baseline settings and require manual handling (which may need to be done separately for each well). The baseline start cycle should be after the initial tailing of background noise and the end cycle should be before the signal shift due to amplification. The range does not have to be too large; around five cycles is sufficient but more is better. If baseline adjustment does not correct the irregularities in amplification curves, the lamp of the instrument may need replacing (a requirement after more than 2000 hours of use for most instruments). See ABI: Setting Baselines and Thresholds.