diff --git a/src/core/clock.ml b/src/core/clock.ml
index 473af440..4a39145c 100644
--- a/src/core/clock.ml
+++ b/src/core/clock.ml
@@ -21,6 +21,7 @@ end
 (** Clock that uses ptime. *)
 let ptime_clock : t = { now = now_ptime_ }
 
+(** Singleton clock *)
 module Main = struct
   open struct
     let main : t Atomic.t = Atomic.make ptime_clock
@@ -28,9 +29,12 @@ module Main = struct
 
   let[@inline] get () = Atomic.get main
 
+  (** Set the current clock *)
   let set t : unit = Util_atomic.update_cas main (fun _ -> (), t)
 
-  (** Clock that always defers to the current main clock *)
+  (** Clock that always defers to the current main clock. Whenever
+      [now dynamic_main] is called, it in turn becomes [now (get ())], ie it
+      looks up the current clock and uses it. *)
   let dynamic_main : t = { now = (fun () -> now (get ())) }
 end