diff --git a/src/main.c b/src/main.c
index a902480..49dc1a2 100644
--- a/src/main.c
+++ b/src/main.c
@@ -104,6 +104,7 @@ int main()
 	printf("Starting VGA sync machine on %u...\n", sm1);
 	vga_hsync_program_init(pio, sm1, offset1);
 	printf("Feeding horizontal sync...\n");
+	// low pulse is X pixels long, and SM runs at 4x of pixel clock
 	pio_sm_put_blocking(pio, sm1, 63 * 4);
 	pio_sm_put_blocking(pio, sm1, 775 * 4);