diff --git a/src/cpu.ml b/src/cpu.ml
index 61e7af5..3b16045 100644
--- a/src/cpu.ml
+++ b/src/cpu.ml
@@ -1,7 +1,7 @@
 (** http://bgb.bircd.org/pandocs.htm#cpuregistersandflags *)
 
 type registers = {
-  a : char;
+  a : char; (* accumulator *)
   b : char;
   c : char;
   d : char;
@@ -9,15 +9,15 @@ type registers = {
   h : char;
   l : char;
 
-  sp : int;
-  pc : int;
+  sp : int; (* stack pointer *)
+  pc : int; (* program counter *)
 }
 
 type flags = {
-  zf : bool;
-  n  : bool;
-  h  : bool;
-  cy : bool;
+  z  : bool; (* zero *)
+  n  : bool; (* substraction *)
+  h  : bool; (* half-carry *)
+  cy : bool; (* carry *)
 }
 
 type t = {