diff --git a/Apple-GCR-disk-encoding.md b/Apple-GCR-disk-encoding.md
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--- a/Apple-GCR-disk-encoding.md
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@@ -1,4 +1,4 @@
-_See https://github.com/TomHarte/dsk2woz/blob/master/dsk2woz.c for an implementation of '6 and 2' disk encoding._
+_See https://github.com/TomHarte/dsk2woz/blob/master/dsk2woz.c#L366 and in particular https://github.com/TomHarte/dsk2woz/blob/master/dsk2woz.c#L308 for an implementation of '6 and 2' disk encoding._
 
 # Physical Encoding
 Apple's GCR encoding was designed in reaction to FM encoding, and uses the same data density and bit clock. However in its more efficient '6 and 2' form it uses only two-thirds as much disk surface area as FM to encode the same data. It predates and is not as efficient as MFM encoding.