Feature: Use real-time "wallclock" timekeeping units (#11341)

src/saveload/afterload.cpp

@@ -735,6 +735,9 @@ bool AfterLoadGame()
 	 * must be done before loading sprites as some newgrfs check it */
 	TimerGameCalendar::SetDate(TimerGameCalendar::date, TimerGameCalendar::date_fract);
 
+	/* Only new games can use wallclock units. */
+	if (IsSavegameVersionBefore(SLV_ECONOMY_MODE_TIMEKEEPING_UNITS)) _settings_game.economy.timekeeping_units = TKU_CALENDAR;
+
 	/* Update economy year. If we don't have a separate economy date saved, follow the calendar date. */
 	if (IsSavegameVersionBefore(SLV_ECONOMY_DATE)) {
 		TimerGameEconomy::SetDate(TimerGameCalendar::date.base(), TimerGameCalendar::date_fract);

src/saveload/saveload.h

@@ -369,6 +369,7 @@ enum SaveLoadVersion : uint16_t {
 
 	SLV_WATER_REGION_EVAL_SIMPLIFIED,       ///< 325  PR#11750 Simplified Water Region evaluation.
 	SLV_ECONOMY_DATE,                       ///< 326  PR#10700 Split calendar and economy timers and dates.
+	SLV_ECONOMY_MODE_TIMEKEEPING_UNITS,     ///< 327  PR#11341 Mode to display economy measurements in wallclock units.
 
 	SL_MAX_VERSION,                         ///< Highest possible saveload version
 };