diff --git a/src/main.rs b/src/main.rs
index 32e1ce2..f1aea66 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -151,13 +151,18 @@ fn main() -> ! {
         w.moder15().output()
     });
 
-    // Configure push-button as input;
+    // Configure push-button (PA0) as input;
     // Configure PA1 as analog-in
     per.gpioa.moder.modify(|_, w| {
         w.moder0().input()
             .moder1().analog()
     });
 
+    // Clear PA3. PA3 can then be a ground reference point for the piezo.
+    // per.gpioa.odr.write(|w| {
+    //     w.odr3().clear_bit()
+    // });
+
     // Configure piezo as digital input
     per.gpiod.moder.modify(|_, w| {
         w.moder0().input()
@@ -193,7 +198,10 @@ fn main() -> ! {
     delay(1000); // >= 10 us
 
     // ADC CALIBRATION (15.3.8)
-    // 1. set ADCALDIF=0 (default)
+    // 1. set ADCALDIF=0 (default) for single-ended cal
+    per.adc1.cr.modify(|_, w| {
+        w.adcaldif().clear_bit()
+    });
 
     // Start cal
     per.adc1.cr.modify(|_, w| {
@@ -214,6 +222,28 @@ fn main() -> ! {
     // wait for ADRDY=1
     while per.adc1.isr.read().adrdy().bit_is_clear() { }
 
+    // Configure sample time (15.3.12)
+    // 0b000 = 1.5 clocks
+    // 0b001 = 2.5 clocks
+    // 0b010 = 4.5 clocks
+    // 0b011 = 7.5 clocks
+    // 0b100 = 19.5 clocks
+    // 0b101 = 61.5 clocks
+    // 0b110 = 181.5 clocks
+    // 0b111 = 601.5 clocks
+    per.adc1.smpr1.modify(|_, w| {
+        unsafe { w.smp1().bits(0b101) };
+        unsafe { w.smp2().bits(0b101) };
+        unsafe { w.smp3().bits(0b101) };
+        unsafe { w.smp4().bits(0b101) };
+        unsafe { w.smp5().bits(0b101) };
+        unsafe { w.smp6().bits(0b101) };
+        unsafe { w.smp7().bits(0b101) };
+        unsafe { w.smp8().bits(0b101) };
+        unsafe { w.smp9().bits(0b101) };
+        w
+    });
+
     // Configure mux'ing: SQRx (regular conversion), JSQRx (injected conversion; don't use these)
     // Draw from ADC1_IN2 -- PA1
     per.adc1.sqr1.modify(|_, w| {