diff --git a/library/include/modules/EventManager.h b/library/include/modules/EventManager.h
index 6f9c69547..80ec77f9d 100644
--- a/library/include/modules/EventManager.h
+++ b/library/include/modules/EventManager.h
@@ -40,8 +40,8 @@ namespace DFHack {
         struct EventHandler {
             typedef void (*callback_t)(color_ostream&, void*); //called when the event happens
             callback_t eventHandler;
-            int32_t freq;
-            int32_t when;
+            int32_t freq; //how often event is allowed to fire (in ticks) use 0 to always fire when possible
+            int32_t when; //when to fire event (global tick count)
 
             EventHandler(callback_t eventHandlerIn, int32_t freqIn): eventHandler(eventHandlerIn), freq(freqIn) {
             }