This dialog defines trimming and processing options for the reads. 
This feature is only available for Sanger sequencing data.
Perform fixed length trimming
Cuts a fixed length from the beginning of the sequence, and cuts the end of the sequence to trim it to a given length.
Perform read 5'/3' trimming
Trims the 5' and/or the 3' read region by base qualities or by occurrences of the ambiguity N. For better assembly results, it is recommended to perform at least trimmings by N's. If both trimming functions are selected, the operations will be performed consecutively.
Read Rejection Thresholds
Three thresholds can be set to define a minimum quality a read must meet to be used in an assembly. If a read does not surpass these thresholds, it will be marked as rejected in the Navigation tree. All thresholds refer to the trimmed sequence, if trimming was enabled.