diff --git a/include/poketch_data.h b/include/poketch_data.h
index 0afafc8e17..5370d0f69c 100644
--- a/include/poketch_data.h
+++ b/include/poketch_data.h
@@ -6,7 +6,7 @@
 
 /** Poketch app IDs, used to register and switch between apps in the Poketch */
 enum PoketchAppID {
-    POKETCH_APPID_DIGITALWATCH,
+    POKETCH_APPID_DIGITALWATCH = 0,
     POKETCH_APPID_CALCULATOR,
     POKETCH_APPID_MEMOPAD,
     POKETCH_APPID_PEDOMETER,
@@ -29,15 +29,15 @@ enum PoketchAppID {
     POKETCH_APPID_KITCHENTIMER,
     POKETCH_APPID_COLORCHANGER,
     POKETCH_APPID_MATCHUPCHECKER,
-    POKETCH_APPID_STOPWATCH,
-    POKETCH_APPID_ALARMCLOCK,
+    POKETCH_APPID_STOPWATCH,            // unused
+    POKETCH_APPID_ALARMCLOCK,           // unused
 
     POKETCH_APPID_MAX
 };
 
 /** Poketch Screen colors, used in PoketchData_SetScreenColor */
 enum PoketchScreenColor {
-    POKETCH_SCREEN_COLOR_GREEN,
+    POKETCH_SCREEN_COLOR_GREEN = 0,
     POKETCH_SCREEN_COLOR_YELLOW,
     POKETCH_SCREEN_COLOR_ORANGE,
     POKETCH_SCREEN_COLOR_RED,
@@ -76,8 +76,9 @@ typedef struct PoketchData {
     u16 unk_28_12 : 4;     //!< unused; bitfield padding
 
     u8 unk_2A[120];
-    u32 unk_A4;
-    u8 unk_A8;
+
+    u32 calendarMarkBitmap;     //!< Bitmap for every day in the calendar month and whether it's been marked
+    u8 calendarMonth;      //!< Current calendar month
 
     /**
     * @brief XY coordinates of a single Map Marker in the Marking Map app
@@ -221,9 +222,36 @@ void PoketchData_AlarmTime(const PoketchData *poketchData, u32 *hour, u32 *minut
  */
 void PoketchData_SetAlarm(PoketchData *poketchData, BOOL enabled, u32 hour, u32 minute);
 
-void sub_02056934(PoketchData *poketchData, u32 param1, u32 param2);
-void sub_02056970(PoketchData *poketchData, u32 param1, u32 param2);
-BOOL sub_020569A8(const PoketchData *poketchData, u32 param1, u32 param2);
+/**
+ * Marks the given date on the Calendar app as highlighted.
+ *
+ * @param poketchData:      The Poketch data to update.
+ * @param month:            The month of the date to mark. If this month does not match the currently stored month, 
+ *                          the month will update to this value and clear all marks on the calendar (except the one on the passed in day).
+ * @param day:              The day of the date to mark.
+ */
+void PoketchData_SetCalendarMark(PoketchData *poketchData, u32 month, u32 day);
+
+/**
+ * Clears the mark on the given date on the Calendar app.
+ *
+ * @param poketchData:      The Poketch data to update.
+ * @param month:            The month of the date to clear. If this month does not match the currently stored month, 
+ *                          the month will update to this value and clear all marks on the calendar.
+ * @param day:              The day of the date to clear.
+ */
+void PoketchData_ClearCalendarMark(PoketchData *poketchData, u32 month, u32 day);
+
+/**
+ * Checks whether the given date is currently marked on the calendar.
+ *
+ * @param poketchData:      The Poketch data to check.
+ * @param month:            The month of the date to check.
+ * @param day:              The day of the date to check.
+ * 
+ * @param return TRUE if the date is marked, FALSE if not. If the given month is not the currently stored month, returns FALSE.
+ */
+BOOL PoketchData_CalendarMarked(const PoketchData *poketchData, u32 month, u32 day);
 
 /**
  * Sets the location of a map marker.
diff --git a/src/overlay050/ov50_022561C0.c b/src/overlay050/ov50_022561C0.c
index 0237a3456d..bccaf4a871 100644
--- a/src/overlay050/ov50_022561C0.c
+++ b/src/overlay050/ov50_022561C0.c
@@ -160,7 +160,7 @@ static void ov50_022562AC (UnkStruct_ov50_02256510_1 * param0, UnkStruct_ov50_02
 
     for (v1 = 0; v1 < (param0->unk_04); v1++) {
         param0->unk_0C[v1].unk_00 = v1 + 1;
-        param0->unk_0C[v1].unk_03 = sub_020569A8(param1->unk_98, param0->unk_00, v1 + 1);
+        param0->unk_0C[v1].unk_03 = PoketchData_CalendarMarked(param1->unk_98, param0->unk_00, v1 + 1);
         param0->unk_0C[v1].unk_02 = v2 + v1;
     }
 }
@@ -252,10 +252,10 @@ static BOOL ov50_02256418 (UnkStruct_ov50_022561D4 * param0)
             if ((param0->unk_A4 >= param0->unk_A8) && (param0->unk_A4 <= param0->unk_AC)) {
                 int v0 = (param0->unk_A4 - param0->unk_A8);
 
-                if (sub_020569A8(param0->unk_98, param0->unk_04.unk_00, v0 + 1)) {
-                    sub_02056970(param0->unk_98, param0->unk_04.unk_00, v0 + 1);
+                if (PoketchData_CalendarMarked(param0->unk_98, param0->unk_04.unk_00, v0 + 1)) {
+                    PoketchData_ClearCalendarMark(param0->unk_98, param0->unk_04.unk_00, v0 + 1);
                 } else {
-                    sub_02056934(param0->unk_98, param0->unk_04.unk_00, v0 + 1);
+                    PoketchData_SetCalendarMark(param0->unk_98, param0->unk_04.unk_00, v0 + 1);
                 }
 
                 param0->unk_04.unk_0C[v0].unk_03 ^= 1;
diff --git a/src/poketch_data.c b/src/poketch_data.c
index 2314faaeb8..a5ca8d559c 100644
--- a/src/poketch_data.c
+++ b/src/poketch_data.c
@@ -43,8 +43,8 @@ void Poketch_Init(PoketchData *poketchData)
     poketchData->alarmSet = 0;
     poketchData->alarmHour = 0;
     poketchData->alarmMinute = 0;
-    poketchData->unk_A8 = 1;
-    poketchData->unk_A4 = 0;
+    poketchData->calendarMonth = 1;
+    poketchData->calendarMarkBitmap = 0;
 
     for (i = 0; i < POKETCH_MAPMARKER_COUNT; i++) {
         poketchData->markMapPositions[i].x = sDefaultMapMarkers[i].x;
@@ -191,33 +191,33 @@ void PoketchData_SetAlarm(PoketchData *poketchData, BOOL enable, u32 hour, u32 m
     poketchData->alarmMinute = minute;
 }
 
-void sub_02056934 (PoketchData *poketchData, u32 param1, u32 param2)
+void PoketchData_SetCalendarMark(PoketchData *poketchData, u32 month, u32 day)
 {
-    if (poketchData->unk_A8 == param1) {
-        poketchData->unk_A4 |= (1 << (param2 - 1));
+    if (poketchData->calendarMonth == month) {
+        poketchData->calendarMarkBitmap |= (1 << (day - 1));
     } else {
-        poketchData->unk_A8 = param1;
-        poketchData->unk_A4 = (1 << (param2 - 1));
+        poketchData->calendarMonth = month;
+        poketchData->calendarMarkBitmap = (1 << (day - 1));
     }
 }
 
-void sub_02056970 (PoketchData *poketchData, u32 param1, u32 param2)
+void PoketchData_ClearCalendarMark(PoketchData *poketchData, u32 month, u32 day)
 {
-    if (poketchData->unk_A8 == param1) {
-        poketchData->unk_A4 &= ~(1 << (param2 - 1));
+    if (poketchData->calendarMonth == month) {
+        poketchData->calendarMarkBitmap &= ~(1 << (day - 1));
     } else {
-        poketchData->unk_A8 = param1;
-        poketchData->unk_A4 = 0;
+        poketchData->calendarMonth = month;
+        poketchData->calendarMarkBitmap = 0;
     }
 }
 
-BOOL sub_020569A8 (const PoketchData *poketchData, u32 param1, u32 param2)
+BOOL PoketchData_CalendarMarked(const PoketchData *poketchData, u32 month, u32 day)
 {
-    if (poketchData->unk_A8 == param1) {
-        return (poketchData->unk_A4 >> (param2 - 1)) & 1;
-    } else {
-        return 0;
+    if (poketchData->calendarMonth == month) {
+        return (poketchData->calendarMarkBitmap >> (day - 1)) & 1;
     }
+
+    return FALSE;
 }
 
 void PoketchData_SetMapMarker(PoketchData *poketchData, int index, u8 x, u8 y)