public virtual ITimeBlock GetPreviousBlock(TimeSpan offset) { var endOff = (offset > TimeSpan.Zero) ? offset.Negate() : offset; var result = new TimeBlock(Duration, Start.Add(endOff), IsReadOnly); if(IsDebugEnabled) log.Debug("이전 Block을 구합니다. offset=[{0}], PreviousBlock=[{1}]", offset, result); return result; }