diff --git a/ubb-la/gui.c b/ubb-la/gui.c
index f73c234..c448471 100644
--- a/ubb-la/gui.c
+++ b/ubb-la/gui.c
@@ -44,6 +44,7 @@
 #define	DIV_RGBA	0x808080ff	/* divisions */
 
 #define	XCENTER		((XRES+CH_XOFF)/2)
+#define	XWIDTH		(XRES-CH_XOFF)
 
 #define	MAP_BUF_Y0	2
 #define	MAP_BUF_Y1	8
@@ -150,7 +151,7 @@ static void show_map(int skip, int nibbles, int s0, int s1)
 	int m = (nibbles+skip) >> 1;
 	int scale = 0;
 
-	while (w >= (XRES-CH_XOFF)/2) {
+	while (w >= XWIDTH/2) {
 		w >>= 1;
 		scale++;
 	}
@@ -351,7 +352,7 @@ static void show_freq(double freq)
 
 static void show_divisions(void)
 {
-	int n = (XRES-CH_XOFF)/2/DIV_X;
+	int n = XWIDTH/2/DIV_X;
 	int i;
 
 	for (i = -n; i <= n; i++)
@@ -377,7 +378,7 @@ void gui(const uint8_t *buf, int skip, int nibbles, double freq)
 	int min_zoom = 0;
 	int i;
 
-	while (XRES-CH_XOFF < (nibbles-skip) >> -min_zoom)
+	while (XWIDTH < (nibbles-skip) >> -min_zoom)
 		min_zoom--;
 	zoom = min_zoom;
 	while (1) {