diff --git a/app/models/schedule_run.rb b/app/models/schedule_run.rb
index c7f2d66..af2ef1a 100644
--- a/app/models/schedule_run.rb
+++ b/app/models/schedule_run.rb
@@ -1,104 +1,133 @@
+# ScheduleRun is a helper class that modelizes the run directives of a schedule
+# resource.
+#
+# It can have 3 levels:
+#
+# * full
+# * differential
+# * incremental
+#
+# Each ScheduleRun instance holds info about the execution time of the schedule:
+#
+# * month specification is optional and is described by:
+#   - month: full name (eg april) | month name three first letters (eg jul)
+#   - month_range: month-month
+#   - monthly: 'monthly'
+# * day specification is required and is described by:
+#   - week_number (optional): weeks number in full text (eg: third, fourth)
+#   - week_range (optional): week_number-week_number
+#   - day: first three letters of day (eg: mon, fri)
+#   - day_range: day-day
+# * time specification is required and is described by:
+#   - 24h time (eg: 03:00)
+#
+# Schedule Run examples:
+#
+#  Level=Full monthly first mon at 12:21
+#  Level=Full first sun at 12:34
+#  Level=Differential second-fifth sat at 15:23
+#  Level=Incremental  mon-sat at 08:00
 class ScheduleRun < ActiveRecord::Base
   enum level: { full: 0, differential: 1, incremental: 2 }
 
   MONTH_KW = %w{jan feb mar apr may jun jul aug sep oct nov dec january february march
                 april may june july august september october november december}
 
   DAYS = (1..31).to_a
   WDAY_KW = %w{mon tue wed thu fri sat sun}
   WEEK_KW = %w{first second third fourth fifth}
 
   belongs_to :schedule
 
   validates :day, :time, :level, presence: true
   validate :correct_chars
   validate :month_valid, if: "month.present?"
   validate :time_valid
   validate :day_valid
 
   # Composes the schedule line for the bacula configuration
   #
   # @return [String]
   def schedule_line
     [ level_to_config, month, day, "at #{time}"].join(" ")
   end
 
   private
 
   def correct_chars
     [:month, :day, :time].each do |x|
       if self.send(x) && self.send(x).to_s.gsub(/[0-9a-zA-Z\-:]/, '').present?
         self.errors.add(x, 'Invalid characters')
       end
     end
   end
 
   def month_valid
     if !month_format? && !valid_month_range?
       self.errors.add(:month, 'Invalid month')
     end
   end
 
   def month_format?
     month_regex = "^(#{MONTH_KW.join('|')}|monthly)$"
     month.match(month_regex).present?
   end
 
   def valid_month_range?
     months = month.split('-')
     return false if months.length != 2
     MONTH_KW.index(months.last) % 12 - MONTH_KW.index(months.first) % 12 > 0
   end
 
   def time_valid
     if !time.match(/^([01][0-9]|2[0-3]):[0-5][0-9]$/)
       self.errors.add(:time, 'Invalid time')
     end
   end
 
   def day_valid
     components = day.split(' ')
     if components.length < 1 || components.length > 2
       self.errors.add(:day, 'Invalid day')
       return false
     end
 
     if !valid_day?(components.last) && !valid_day_range?(components.last)
       self.errors.add(:day, 'Invalid day')
       return false
     end
 
     if components.length == 2 && !valid_week?(components.first) &&
         !valid_week_range?(components.first)
       self.errors.add(:day, 'Invalid day')
       return false
     end
     true
   end
 
   def valid_day?(a_day)
     WDAY_KW.include? a_day
   end
 
   def valid_day_range?(a_range)
     days = a_range.split('-')
     return false if days.length != 2
 
     WDAY_KW.index(days.last) - WDAY_KW.index(days.first) > 0
   end
 
   def valid_week?(a_week)
     WEEK_KW.include? a_week
   end
 
   def valid_week_range?(a_range)
     weeks = a_range.split('-')
     return false if weeks.length != 2
 
     WEEK_KW.index(weeks.last) - WEEK_KW.index(weeks.first) > 0
   end
 
   def level_to_config
     "Level=#{level.capitalize}"
   end
 end