diff --git a/packages/hal/src/validators/apex/denominations.ts b/packages/hal/src/validators/apex/denominations.ts
index 9874da4..95410ed 100644
--- a/packages/hal/src/validators/apex/denominations.ts
+++ b/packages/hal/src/validators/apex/denominations.ts
@@ -1,19 +1,29 @@
 /**
  * Pyramid Apex Denomination Tables
  *
- * The Apex RS-232 reply reports a 1-based CREDIT CHANNEL (1..7), not a value —
- * the channel→value mapping is fixed by the bill dataset programmed into the
- * acceptor's firmware for its country. The arrays below are ascending value
- * lists indexed by (channel - 1); they MUST match the dataset flashed on your
- * specific Apex 7600, or a credited note will be booked at the wrong value.
- * Verify against the unit's configuration card during bring-up.
+ * Indexed by (credit channel - 1). The channel is NOT an index into "the notes
+ * this unit happens to have enabled" — it is a fixed protocol constant.
+ * Pyramid's RS-232 spec (Rev G, "Data Fields for Messages sent by the Slave",
+ * BYTE 2 bits 3-5) fixes the USD mapping:
  *
- * Defaults follow Pyramid's standard datasets (US = $1/$5/$10/$20/$50/$100;
- * $2 channel omitted as it's rarely enabled).
+ *   001 = $1    010 = $2    011 = $5    100 = $10
+ *   101 = $20   110 = $50   111 = $100
+ *
+ * $2 occupies channel 2 whether or not the unit accepts $2 notes. An earlier
+ * version of this table omitted it as "rarely enabled", which shifted every
+ * larger note down one slot: a $5 credited as $10, a $20 as $50, a $50 as
+ * $100, and a $100 as nothing at all. Never drop an unused channel from these
+ * arrays — pad it instead.
+ *
+ * For non-USD the spec says only "Foreign currencies are in sequential order
+ * as note 1-7", so channel N is the Nth note type of whatever dataset is
+ * flashed on the unit. The orderings below are the conventional ascending sets
+ * and are UNVERIFIED against a real configuration card. Check the card before
+ * a machine takes money in any of them.
  */
 
 export const denominations: Record<string, number[]> = {
-  USD: [1, 5, 10, 20, 50, 100],
+  USD: [1, 2, 5, 10, 20, 50, 100],
   EUR: [5, 10, 20, 50, 100, 200, 500],
   GBP: [5, 10, 20, 50],
   CAD: [5, 10, 20, 50, 100],