diff --git a/src/client.ts b/src/client.ts
index fe9e022..fb064fe 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -3,7 +3,6 @@ import DataManager from './data'
 import School from './models/School'
 import type Timetable from './models/Timetable'
 import { encodeBase64, encodeEUCKR } from './utils/encode'
-import { log10int } from './utils/math'
 import { parseResponse } from './utils/parse'
 import axios from 'axios'
 
@@ -57,15 +56,20 @@ export default class Comcigan {
     const teachersLen = Math.floor(Math.log10(teachers.length - 1)) + 1
     const subjects = data[`자료${subjectCode}`] as string[]
 
-    return (data[`자료${dayCode}`] as number[][][][]).slice(1).map((grade) =>
-      grade.slice(1).map((cls) =>
-        cls.slice(1).map((day) =>
-          day.slice(1).map((period) => {
+    const original = data[`자료${originalCode}`] as number[][][][]
+    const day = data[`자료${dayCode}`] as number[][][][]
+
+    return day.slice(1).map((grade, gIdx) =>
+      grade.slice(1).map((cls, cIdx) =>
+        cls.slice(1).map((day, dIdx) =>
+          day.slice(1).map((period, pIdx) => {
             const p = period.toString()
 
             return {
               subject: subjects[Number(p.slice(0, p.length - teachersLen - 1))],
               teacher: teachers[Number(p.slice(-teachersLen))],
+              changed:
+                period !== original[gIdx + 1][cIdx + 1][dIdx + 1][pIdx + 1],
             }
           }),
         ),
diff --git a/src/constants.ts b/src/constants.ts
index 42cefb5..b012054 100644
--- a/src/constants.ts
+++ b/src/constants.ts
@@ -8,6 +8,7 @@ export const RegExes = {
   SearchRoute: /(?<=\?)\d+(?=l)/,
   TimetableRoute: /(?<=')\d+(?=_')/,
   TeacherCode: /(?<=성명=자료\.자료)\d+/,
+  OriginalCode: /(?<=원자료=Q자료\(자료.자료)\d+/,
   DayCode: /(?<=일일자료=Q자료\(자료.자료)\d+/,
   SubjectCode: /(?<=자료.자료)\d+(?=\[sb\])/,
   WhiteSpace: /\0+$/,
diff --git a/src/data.ts b/src/data.ts
index 65f9fa1..8f900a7 100644
--- a/src/data.ts
+++ b/src/data.ts
@@ -8,6 +8,7 @@ interface Data {
   timetableRoute: string
 
   teacherCode: string
+  originalCode: string
   dayCode: string
   subjectCode: string
 }
@@ -37,6 +38,9 @@ export default class DataManager {
     const teacher = RegExes.TeacherCode.exec(data)
     if (!teacher) throw new Error('Failed to fetch teacher code')
 
+    const original = RegExes.OriginalCode.exec(data)
+    if (!original) throw new Error('Failed to fetch original code')
+
     const day = RegExes.DayCode.exec(data)
     if (!day) throw new Error('Failed to fetch day code')
 
@@ -49,6 +53,7 @@ export default class DataManager {
       searchRoute: search[0],
       timetableRoute: timetable[0],
       teacherCode: teacher[0],
+      originalCode: original[0],
       dayCode: day[0],
       subjectCode: subject[0],
     }