diff --git a/core/src/cpu/operations.rs b/core/src/cpu/operations.rs
index c4e351e..b248c97 100644
--- a/core/src/cpu/operations.rs
+++ b/core/src/cpu/operations.rs
@@ -1,6 +1,8 @@
 use crate::cpu::op::Operand;
 use crate::cpu::{Cpu, CpuInternals, CpuStatus};
 
+// Unofficial ops documentation: https://www.masswerk.at/6502/6502_instruction_set.html#SAX
+
 fn is_sign_overflow(val1: u8, val2: u8, result: u8) -> bool {
     (val1 & 0x80 == val2 & 0x80) && (val1 & 0x80 != result & 0x80)
 }