diff --git a/src/order_func.h b/src/order_func.h
--- a/src/order_func.h
+++ b/src/order_func.h
@@ -26,10 +26,16 @@ uint GetOrderDistance(const Order *prev,
 
 void DrawOrderString(const Vehicle *v, const Order *order, int order_index, int y, bool selected, bool timetable, int left, int middle, int right);
 
-#define MIN_SERVINT_PERCENT  5
-#define MAX_SERVINT_PERCENT 90
-#define MIN_SERVINT_DAYS    30
-#define MAX_SERVINT_DAYS   800
+static const uint DEF_SERVINT_DAYS_TRAINS   = 150;
+static const uint DEF_SERVINT_DAYS_ROADVEH  = 150;
+static const uint DEF_SERVINT_DAYS_AIRCRAFT = 100;
+static const uint DEF_SERVINT_DAYS_SHIPS    = 360;
+static const uint MIN_SERVINT_DAYS          = 30;
+static const uint MAX_SERVINT_DAYS          = 800;
+
+static const uint DEF_SERVINT_PERCENT = 50;
+static const uint MIN_SERVINT_PERCENT = 5;
+static const uint MAX_SERVINT_PERCENT = 90;
 
 uint16 GetServiceIntervalClamped(uint interval, bool ispercent);
 
diff --git a/src/settings_table.cpp b/src/settings_table.cpp
--- a/src/settings_table.cpp
+++ b/src/settings_table.cpp
@@ -127,7 +127,10 @@ static void UpdateConsists(int32 new_val
 	InvalidateWindowClassesData(WC_BUILD_VEHICLE, 0);
 }
 
-/* Check service intervals of vehicles, newvalue is value of % or day based servicing */
+/**
+ * Check and update if needed all vehicle service intervals.
+ * @param new_value Contains 0 if service intervals are in days, otherwise intervals use percents.
+ */
 static void UpdateAllServiceInterval(int32 new_value)
 {
 	bool update_vehicles;
@@ -141,15 +144,17 @@ static void UpdateAllServiceInterval(int
 	}
 
 	if (new_value != 0) {
-		vds->servint_trains   = 50;
-		vds->servint_roadveh  = 50;
-		vds->servint_aircraft = 50;
-		vds->servint_ships    = 50;
+		/* Service intervals are in percents. */
+		vds->servint_trains   = DEF_SERVINT_PERCENT;
+		vds->servint_roadveh  = DEF_SERVINT_PERCENT;
+		vds->servint_aircraft = DEF_SERVINT_PERCENT;
+		vds->servint_ships    = DEF_SERVINT_PERCENT;
 	} else {
-		vds->servint_trains   = 150;
-		vds->servint_roadveh  = 150;
-		vds->servint_aircraft = 100;
-		vds->servint_ships    = 360;
+		/* Service intervals are in days. */
+		vds->servint_trains   = DEF_SERVINT_DAYS_TRAINS;
+		vds->servint_roadveh  = DEF_SERVINT_DAYS_ROADVEH;
+		vds->servint_aircraft = DEF_SERVINT_DAYS_AIRCRAFT;
+		vds->servint_ships    = DEF_SERVINT_DAYS_SHIPS;
 	}
 
 	if (update_vehicles) {
diff --git a/src/table/settings/company_settings.ini b/src/table/settings/company_settings.ini
--- a/src/table/settings/company_settings.ini
+++ b/src/table/settings/company_settings.ini
@@ -83,9 +83,10 @@ post_cb  = UpdateAllServiceInterval
 var      = vehicle.servint_trains
 type     = SLE_UINT16
 flags    = SF_PER_COMPANY | SF_GUI_0_IS_SPECIAL
-def      = 150
-min      = 5
-max      = 800
+def      = DEF_SERVINT_DAYS_TRAINS
+min      = MIN_SERVINT_PERCENT
+max      = MAX_SERVINT_DAYS
+interval = 1
 str      = STR_CONFIG_SETTING_SERVINT_TRAINS
 strhelp  = STR_CONFIG_SETTING_SERVINT_TRAINS_HELPTEXT
 strval   = STR_CONFIG_SETTING_SERVINT_VALUE
@@ -96,9 +97,10 @@ post_cb  = [](auto new_value) { UpdateSe
 var      = vehicle.servint_roadveh
 type     = SLE_UINT16
 flags    = SF_PER_COMPANY | SF_GUI_0_IS_SPECIAL
-def      = 150
-min      = 5
-max      = 800
+def      = DEF_SERVINT_DAYS_ROADVEH
+min      = MIN_SERVINT_PERCENT
+max      = MAX_SERVINT_DAYS
+interval = 1
 str      = STR_CONFIG_SETTING_SERVINT_ROAD_VEHICLES
 strhelp  = STR_CONFIG_SETTING_SERVINT_ROAD_VEHICLES_HELPTEXT
 strval   = STR_CONFIG_SETTING_SERVINT_VALUE
@@ -109,9 +111,10 @@ post_cb  = [](auto new_value) { UpdateSe
 var      = vehicle.servint_ships
 type     = SLE_UINT16
 flags    = SF_PER_COMPANY | SF_GUI_0_IS_SPECIAL
-def      = 360
-min      = 5
-max      = 800
+def      = DEF_SERVINT_DAYS_SHIPS
+min      = MIN_SERVINT_PERCENT
+max      = MAX_SERVINT_DAYS
+interval = 1
 str      = STR_CONFIG_SETTING_SERVINT_SHIPS
 strhelp  = STR_CONFIG_SETTING_SERVINT_SHIPS_HELPTEXT
 strval   = STR_CONFIG_SETTING_SERVINT_VALUE
@@ -122,9 +125,10 @@ post_cb  = [](auto new_value) { UpdateSe
 var      = vehicle.servint_aircraft
 type     = SLE_UINT16
 flags    = SF_PER_COMPANY | SF_GUI_0_IS_SPECIAL
-def      = 100
-min      = 5
-max      = 800
+def      = DEF_SERVINT_DAYS_AIRCRAFT
+min      = MIN_SERVINT_PERCENT
+max      = MAX_SERVINT_DAYS
+interval = 1
 str      = STR_CONFIG_SETTING_SERVINT_AIRCRAFT
 strhelp  = STR_CONFIG_SETTING_SERVINT_AIRCRAFT_HELPTEXT
 strval   = STR_CONFIG_SETTING_SERVINT_VALUE