diff --git a/firmware/calibrate.c b/firmware/calibrate.c
index be3afa2..7300a8e 100644
--- a/firmware/calibrate.c
+++ b/firmware/calibrate.c
@@ -5,13 +5,14 @@
 #include "dac.h"
 #include "led.h"
 #include "timer.h"
+#include "uart.h"
 
 float g_scale;  /* delta(DAC) / delta(ADC) */
 
 /* Initialize.  Assume some relatively-safe scaling if no calibration is run */
 void calibrate_init(void)
 {
-	g_scale = 0.1;  /* 1 count at DAC means 10 counts at ADC */
+	g_scale = 0.5;  /* 1 count at DAC means 4 counts at ADC */
 }
 
 /* Given the current DAC and ADC values d1 and a1,
@@ -22,7 +23,7 @@ uint16_t adc_to_dac(uint16_t d1, int16_t a1, int16_t a2, float scale)
 	int32_t d2;
 
 	delta = (int32_t)((a2 - a1) * scale + 0.5);
-	d2 = d1 - delta;
+	d2 = d1 + delta;
 	return clamp(DAC_MIN, d2, DAC_MAX);
 }
 
@@ -32,7 +33,7 @@ float calculate_scale(uint16_t d1, float a1, uint16_t d2, float a2)
 	if (d1 == d2)
 		return 1.0;
 	else
-		return (a2 - a1) / (float)(d2 - d1);
+		return (a2 - a1) / ((float)d2 - d1);
 }
 
 /* Seek with the DAC to reach a specific ADC value.  Uses g_scale as
@@ -55,7 +56,7 @@ uint16_t seek(uint16_t starting_dac, int16_t desired_adc)
 	{
 		/* give up if we're not making progress */
 		if (steps++ > SEEK_MAX_STEPS) {
-			led_pattern(0b00000001);
+			led_pattern(0b00101000);
 			break;
 		}
 
@@ -70,9 +71,21 @@ uint16_t seek(uint16_t starting_dac, int16_t desired_adc)
 		msleep(1);
 		adc = adc_get();
 
+#if 0
+		uart1_put_hex16(dac);
+		uart1_put(' ');
+		uart1_put_hex16(adc);
+		uart1_put(' ');
+		uart1_put_hex16(desired_adc);
+		uart1_put(' ');
+		uart1_put_hex32(*(uint32_t *)&scale);
+		uart1_crlf();
+#endif
+
 		/* if we're close, accept it */
-		if (abs(adc - desired_adc) <= SEEK_FUZZ_ADC)
+		if (abs(adc - desired_adc) <= SEEK_FUZZ_ADC) {
 			break;
+		}
 
 		/* otherwise, if we were within ADC clamp limits, and
 		   the DAC changed a non-trivial amount, readjust
@@ -95,7 +108,7 @@ uint16_t seek(uint16_t starting_dac, int16_t desired_adc)
 }
 
 /* Perform calibration */
-float do_calibrate(void)
+uint16_t do_calibrate(void)
 {
 	uint16_t daczero, x1, x2;
 	float y1, y2;
@@ -103,18 +116,35 @@ float do_calibrate(void)
 	/* Zero ADC */
 	daczero = seek((DAC_MIN + DAC_MAX) / 2, CALIBRATE_ADC_ZERO);
 
-	/* Go halfway down and take an accurate sample */
+	/* Go down take an accurate sample */
 	x1 = seek(daczero, CALIBRATE_ADC_LOW);
 	y1 = oversample(x1);
 
-	/* Go halfway up and take an accurate sample */
+	/* Go up and take an accurate sample */
 	x2 = seek(daczero, CALIBRATE_ADC_HIGH);
 	y2 = oversample(x2);
 
 	/* Calculate scale */
 	g_scale = calculate_scale(x1, y1, x2, y2);
 
-	return g_scale;
+#if 1
+	uart1_put_string("calibrate x1=");
+	uart1_put_dec(x1);
+	uart1_put_string(" y1=");
+	uart1_put_float(y1);
+	uart1_put_string(" x2=");
+	uart1_put_dec(x2);
+	uart1_put_string(" y2=");
+	uart1_put_float(y2);
+	uart1_put_string(" scale=");
+	uart1_put_float(g_scale);
+	uart1_crlf();
+#endif
+
+	/* Return to zero position */
+	dac_write(daczero);
+
+	return daczero;
 }
 
 /* Oversample to get a nice ADC value */
diff --git a/firmware/calibrate.h b/firmware/calibrate.h
index b2664d6..010d880 100644
--- a/firmware/calibrate.h
+++ b/firmware/calibrate.h
@@ -7,10 +7,10 @@
 #define DAC_MIN 0
 #define DAC_MAX 65535
 
-#define OVERSAMPLE_COUNT 128
+#define OVERSAMPLE_COUNT 256
 
 #define SEEK_MAX_STEPS 1000
-#define SEEK_FUZZ_ADC 20
+#define SEEK_FUZZ_ADC 10
 #define SEEK_FUZZ_DAC 5
 
 #define CALIBRATE_ADC_ZERO 1024
@@ -32,7 +32,7 @@ float calculate_scale(uint16_t d1, float a1, uint16_t d2, float a2);
 uint16_t seek(uint16_t starting_dac, int16_t desired_adc);
 
 /* Perform calibration */
-float do_calibrate(void);
+uint16_t do_calibrate(void);
 
 /* Oversample to get a nice ADC value */
 float oversample(uint16_t dac);
diff --git a/firmware/led.h b/firmware/led.h
index d5e1e66..c01520a 100644
--- a/firmware/led.h
+++ b/firmware/led.h
@@ -3,7 +3,7 @@
 
 #include "config.h"
 
-#define LED_BLINK_RATE 4
+#define LED_BLINK_RATE 8
 extern int16_t __led_pattern;
 
 /* Initialize LED */
diff --git a/firmware/mode_debug.c b/firmware/mode_debug.c
index 97ce744..ab83d6c 100644
--- a/firmware/mode_debug.c
+++ b/firmware/mode_debug.c
@@ -121,28 +121,21 @@ void run_debug(void)
 		// test seeking
 		case '1':
 			uart1_put_string("seek 512\r\n");
-			while (!uart1_can_get())
-				dac = seek(dac, 512);
-			uart1_get();
+			dac = seek(dac, 512);
 			break;
 
 		case '2':
 			uart1_put_string("seek 1536\r\n");
-			while (!uart1_can_get())
-				dac = seek(dac, 1536);
-			uart1_get();
+			dac = seek(dac, 1536);
 			break;
 
 		// run calibration
 		case 'c':
 		case 'C':
-			uart1_put_string("old g_scale ");
-			uart1_put_hex32(*(uint32_t *)&g_scale);
-			uart1_crlf();
 			uart1_put_string("calibrating...\r\n");
-			do_calibrate();
+			dac = do_calibrate();
 			uart1_put_string("new g_scale ");
-			uart1_put_hex32(*(uint32_t *)&g_scale);
+			uart1_put_float(g_scale);
 			uart1_crlf();
 			break;
 
diff --git a/firmware/uart.c b/firmware/uart.c
index aa5aa87..1c05cbb 100644
--- a/firmware/uart.c
+++ b/firmware/uart.c
@@ -121,6 +121,22 @@ void uart_put_dec(int uart, int32_t x)
 	}
 }
 
+void uart_put_float(int uart, float x)
+{
+	int i;
+	int32_t v;
+
+	v = (int32_t) x;
+	uart_put_dec(uart, v);
+	uart_put(uart, '.');
+	for (i = 0; i < 6; i++) {
+		x -= v;
+		x *= 10;
+		v = (int32_t) x;
+		uart_put(uart, v + '0');
+	}
+}
+
 void uart_crlf(int uart)
 {
 	uart_put(uart, '\r');
diff --git a/firmware/uart.h b/firmware/uart.h
index 24368a7..26edb43 100644
--- a/firmware/uart.h
+++ b/firmware/uart.h
@@ -15,6 +15,7 @@ void uart_put_hex16(int uart, uint16_t x);
 void uart_put_hex32(int uart, uint32_t x);
 void uart_put_bin(int uart, uint8_t x);
 void uart_put_dec(int uart, int32_t x);
+void uart_put_float(int uart, float x);
 
 /* Blocking receives */
 uint8_t uart_get(int uart);
@@ -35,6 +36,7 @@ int uart_can_put(int uart);
 #define uart1_put_hex32(x)	uart_put_hex32(1,x)
 #define uart1_put_bin(x)	uart_put_bin(1,x)
 #define uart1_put_dec(x)	uart_put_dec(1,x)
+#define uart1_put_float(x)	uart_put_float(1,x)
 
 #define uart2_init(x) 		uart_init(2, x)
 #define uart2_can_get() 	uart_can_get(2)
@@ -47,5 +49,6 @@ int uart_can_put(int uart);
 #define uart2_put_hex32(x)	uart_put_hex32(2,x)
 #define uart2_put_bin(x)	uart_put_bin(2,x)
 #define uart2_put_dec(x)	uart_put_dec(2,x)
+#define uart2_put_float(x)	uart_put_float(2,x)
 
 #endif
diff --git a/firmware/util.h b/firmware/util.h
index fe91d45..3c55022 100644
--- a/firmware/util.h
+++ b/firmware/util.h
@@ -36,6 +36,6 @@ int32_t hex_to_u16(char x[4]);
 
 #define abs(a)					\
     ({ typeof (a) _a = (a);			\
-       _a < 0 ? _a : -_a; })
+       _a < 0 ? -_a : _a; })
 
 #endif
diff --git a/firmware/zoom.c b/firmware/zoom.c
index c1b2d74..ee2da8a 100644
--- a/firmware/zoom.c
+++ b/firmware/zoom.c
@@ -8,6 +8,7 @@
 #include "led.h"
 #include "mode.h"
 #include "zoom.h"
+#include "calibrate.h"
 
 int main(void)
 {
@@ -16,6 +17,7 @@ int main(void)
 	config_init();
 	led_init();
 	led_on();	
+	calibrate_init();
 
 	/* debug output */
 	TRISAbits.TRISA9 = 0;