Here is the code to turn the Circuit Playground into an inclinometer. Copy and paste it into the Arduino IDE, load it on to the Circuit Playground, and go the next page to learn how to use it.

///////////////////////////////////////////////////////////////////////////////
// Circuit Playground How Tall Is It
//
// Uses the accelerometer to turn the Circuit Playground into an inclinometer.
// Can be used to determine the height of objects using a little right angle
// math.
//
// Author: Carter Nelson
// MIT License (https://opensource.org/licenses/MIT)
#include <Adafruit_CircuitPlayground.h>
#include <Wire.h>
#include <SPI.h>
float X, Y, Z;
float angle;
float totalAccel;
bool goodReading;
uint8_t angleDisplay;
///////////////////////////////////////////////////////////////////////////////
void setup()
{
// Initialize Circuit Playground library.
CircuitPlayground.begin();
// Set the accelerometer range.
CircuitPlayground.setAccelRange(LIS3DH_RANGE_2_G);
// Indicate ready using NeoPixel 9.
// Set it red to indicate no good reading yet.
CircuitPlayground.setPixelColor(9, 255, 0, 0);
}
///////////////////////////////////////////////////////////////////////////////
void loop()
{
// Only take action when either button is pressed.
if ( (CircuitPlayground.leftButton() == true) ||
(CircuitPlayground.rightButton() == true) ) {
// Average several readings.
X = 0.0;
Y = 0.0;
Z = 0.0;
for (int i=0; i<10; i=i+1) {
X = X + CircuitPlayground.motionX();
Y = Y + CircuitPlayground.motionY();
Z = Z + CircuitPlayground.motionZ();
delay(10);
}
X = X / 10.0;
Y = Y / 10.0;
Z = Z / 10.0;
// Compute angle.
#ifdef __AVR__ // Circuit Playground Classic
angle = atan2(Y, X);
#else // Circuit Playground Express
angle = atan2(-X, Y);
#endif
// Compute total acceleration
totalAccel = sqrt(X*X + Y*Y + Z*Z);
// Initially assume the reading is good.
goodReading = true;
// Check for levelness.
// Ideally Z=0, but allow a small amount of Z.
if (abs(Z) > 1.0) {
goodReading = false;
}
// Check for motion.
// Gravity (9.8 m/s^2) should be the only acceleration, but allow a small amount of motion.
if (totalAccel > 10.0) {
goodReading = false;
}
// Indicate if reading was good.
if (goodReading == true) {
// Green light.
CircuitPlayground.setPixelColor(9, 0, 255, 0);
} else {
// Red light.
CircuitPlayground.setPixelColor(9, 255, 0, 0);
}
// Indicate sign of angle.
if (angle < 0) {
// Blue light.
CircuitPlayground.setPixelColor(8, 0, 0, 255);
} else {
// Off.
CircuitPlayground.setPixelColor(8, 0, 0, 0);
}
// Display angle magnitude, in degrees, on NeoPixels 0-7 as 8 bit value.
// 1 = NeoPixel ON, 0 = NeoPixel OFF
// First, convert the angle to degrees and make integer.
angleDisplay = uint8_t(abs(angle * 57.29578));
// Now display one bit at a time
for (int p=0; p<8; p=p+1) {
// Is the least signficant bit a 1?
if (angleDisplay & 0x01 == 1) {
// Turn on the NeoPixel
CircuitPlayground.setPixelColor(p, 255, 255, 255);
} else {
// Turn off the NeoPixel
CircuitPlayground.setPixelColor(p, 0, 0, 0);
}
// Shift the value down to the next bit.
angleDisplay = angleDisplay >> 1;
}
}
}

///////////////////////////////////////////////////////////////////////////////
// Circuit Playground How Tall Is It
//
// Uses the accelerometer to turn the Circuit Playground into an inclinometer.
// Can be used to determine the height of objects using a little right angle
// math.
//
// Author: Carter Nelson
// MIT License (https://opensource.org/licenses/MIT)
#include <Adafruit_CircuitPlayground.h>
#include <Wire.h>
#include <SPI.h>
float X, Y, Z;
float angle;
float totalAccel;
bool goodReading;
uint8_t angleDisplay;
///////////////////////////////////////////////////////////////////////////////
void setup()
{
// Initialize Circuit Playground library.
CircuitPlayground.begin();
// Set the accelerometer range.
CircuitPlayground.setAccelRange(LIS3DH_RANGE_2_G);
// Indicate ready using NeoPixel 9.
// Set it red to indicate no good reading yet.
CircuitPlayground.setPixelColor(9, 255, 0, 0);
}
///////////////////////////////////////////////////////////////////////////////
void loop()
{
// Only take action when either button is pressed.
if ( (CircuitPlayground.leftButton() == true) ||
(CircuitPlayground.rightButton() == true) ) {
// Average several readings.
X = 0.0;
Y = 0.0;
Z = 0.0;
for (int i=0; i<10; i=i+1) {
X = X + CircuitPlayground.motionX();
Y = Y + CircuitPlayground.motionY();
Z = Z + CircuitPlayground.motionZ();
delay(10);
}
X = X / 10.0;
Y = Y / 10.0;
Z = Z / 10.0;
// Compute angle.
#ifdef __AVR__ // Circuit Playground Classic
angle = atan2(Y, X);
#else // Circuit Playground Express
angle = atan2(-X, Y);
#endif
// Compute total acceleration
totalAccel = sqrt(X*X + Y*Y + Z*Z);
// Initially assume the reading is good.
goodReading = true;
// Check for levelness.
// Ideally Z=0, but allow a small amount of Z.
if (abs(Z) > 1.0) {
goodReading = false;
}
// Check for motion.
// Gravity (9.8 m/s^2) should be the only acceleration, but allow a small amount of motion.
if (totalAccel > 10.0) {
goodReading = false;
}
// Indicate if reading was good.
if (goodReading == true) {
// Green light.
CircuitPlayground.setPixelColor(9, 0, 255, 0);
} else {
// Red light.
CircuitPlayground.setPixelColor(9, 255, 0, 0);
}
// Indicate sign of angle.
if (angle < 0) {
// Blue light.
CircuitPlayground.setPixelColor(8, 0, 0, 255);
} else {
// Off.
CircuitPlayground.setPixelColor(8, 0, 0, 0);
}
// Display angle magnitude, in degrees, on NeoPixels 0-7 as 8 bit value.
// 1 = NeoPixel ON, 0 = NeoPixel OFF
// First, convert the angle to degrees and make integer.
angleDisplay = uint8_t(abs(angle * 57.29578));
// Now display one bit at a time
for (int p=0; p<8; p=p+1) {
// Is the least signficant bit a 1?
if (angleDisplay & 0x01 == 1) {
// Turn on the NeoPixel
CircuitPlayground.setPixelColor(p, 255, 255, 255);
} else {
// Turn off the NeoPixel
CircuitPlayground.setPixelColor(p, 0, 0, 0);
}
// Shift the value down to the next bit.
angleDisplay = angleDisplay >> 1;
}
}
}