diff --git a/dailyAverage.js b/dailyAverage.js
index ee42fb2..df80ec2 100644
--- a/dailyAverage.js
+++ b/dailyAverage.js
@@ -5,8 +5,8 @@ import { trimDate } from "./trimDate.js";
  * Calculates daily averages for the time series specified by `datetime` and `x`.
  *
  * The returned object contains two properties:
- * * datetime -- an array of date objects specifying the starting hour of each day
- * * avg -- an array daily average values for each day
+ * * datetime -- Array of date objects specifying the starting hour of each day
+ * * average -- Array or daily average values for each day
  * @param {...Date} datetime Regular hourly axis representing the time associated
  * with each measurement.
  * @param {...Number} x Array of hourly measurements.
@@ -21,19 +21,19 @@ export function dailyAverage(datetime, x, timezone) {
 
   let dayCount = trimmed.datetime.length / 24;
   let daily_datetime = [];
-  let daily_avg = [];
+  let daily_average = [];
   for (let i = 0; i < dayCount; i++) {
     let start = i * 24;
     let end = i * 24 + 24;
     // NOTE:  Average is assigned to the start of the day.
     daily_datetime[i] = trimmed.datetime[start];
-    daily_avg[i] = trimmed.x.slice(start, end).reduce((a, o) => a + o) / 24;
+    daily_average[i] = trimmed.x.slice(start, end).reduce((a, o) => a + o) / 24;
   }
 
   // Round to one decimal place and ensure null is the missing value
-  daily_avg = daily_avg.map((o) =>
+  daily_average = daily_average.map((o) =>
     o === null || o === undefined || isNaN(o) ? null : Math.round(10 * o) / 10
   );
 
-  return { datetime: daily_datetime, avg: daily_avg };
+  return { datetime: daily_datetime, average: daily_average };
 }
diff --git a/diurnalAverage.js b/diurnalAverage.js
index 2796d9b..af4c8b0 100644
--- a/diurnalAverage.js
+++ b/diurnalAverage.js
@@ -6,7 +6,7 @@ import { trimDate } from "./trimDate.js";
  *
  * The returned object contains two properties:
  * * hour -- Array of local time hours [0-24]
- * * avg -- Array of time-of-day averages for each hour
+ * * average -- Array of time-of-day averages for each hour
  *
  * By default, the averages are calculated using data from the most recent 7 days
  * in the `datetime` array.
@@ -28,7 +28,7 @@ export function diurnalAverage(datetime, x, timezone, dayCount = 7) {
   let hours = localTime.map((o) => o.hours());
 
   let hour = [];
-  let hourly_avg = [];
+  let hourly_average = [];
 
   // For each hour, average together the contributions from each day
   for (let h = 0; h < 24; h++) {
@@ -37,13 +37,13 @@ export function diurnalAverage(datetime, x, timezone, dayCount = 7) {
       sum += x[h + d * 24];
     }
     hour[h] = h;
-    hourly_avg[h] = sum / dayCount;
+    hourly_average[h] = sum / dayCount;
   }
 
   // Round to one decimal place and ensure null is the missing value
-  hourly_avg = hourly_avg.map((o) =>
+  hourly_average = hourly_average.map((o) =>
     o === null || o === undefined || isNaN(o) ? null : Math.round(10 * o) / 10
   );
 
-  return { hour: hour, avg: hourly_avg };
+  return { hour: hour, average: hourly_average };
 }
diff --git a/tests/dailyAverage.test.js b/tests/dailyAverage.test.js
new file mode 100644
index 0000000..ed7deb4
--- /dev/null
+++ b/tests/dailyAverage.test.js
@@ -0,0 +1,49 @@
+import { test } from "uvu";
+import * as assert from "uvu/assert";
+
+import moment from "moment-timezone";
+import { dailyAverage } from "../index.js";
+
+// Start of Valentine's Day in Greenwich
+let start = moment.tz("2023-02-14 00:00:00", "UTC");
+let datetime = [];
+let x = [];
+
+// Precisely 10 days worth of data
+let day = 0;
+for (var i = 0; i < 240; i++) {
+  if (i % 24 === 0) day++;
+  datetime[i] = new Date(start + i * 3600 * 1000);
+  let val = day * 10 + 5 * Math.sin((i * Math.PI) / 12);
+  x[i] = Math.round(val * 10) / 10;
+}
+
+test("daily averages work for 'UTC'", () => {
+  let timezone = "UTC";
+  let daily = dailyAverage(datetime, x, timezone);
+  let day0 = new Date(moment.tz("2023-02-14 00:00:00", "UTC"));
+  let day1 = new Date(moment.tz("2023-02-15 00:00:00", "UTC"));
+  assert.equal(daily.datetime.slice(0, 2), [day0, day1]);
+  assert.equal(daily.average.slice(0, 2), [10, 20]);
+});
+
+test("daily averages work for 'America/Chicago'", () => {
+  let timezone = "America/Chicago";
+  let daily = dailyAverage(datetime, x, timezone);
+  let day0 = new Date(moment.tz("2023-02-14 06:00:00", "UTC"));
+  let day1 = new Date(moment.tz("2023-02-15 06:00:00", "UTC"));
+  assert.equal(daily.datetime.slice(0, 2), [day0, day1]);
+  assert.equal(daily.average.slice(0, 2), [12.5, 22.5]);
+});
+
+// ----- Run all tests ---------------------------------------------------------
+
+test.run();
+
+// ----- Notes -----------------------------------------------------------------
+
+// // Manual testing for "America/Chicago"
+// x.slice(6,30).reduce((a,o) => a + o) / 24
+// // 12.5
+// x.slice(30,54).reduce((a,o) => a + o) / 24
+// // 22.5
diff --git a/tests/demo.js b/tests/demo.js
deleted file mode 100644
index 4432ab4..0000000
--- a/tests/demo.js
+++ /dev/null
@@ -1,23 +0,0 @@
-// tests/demo.js
-import { test } from "uvu";
-import * as assert from "uvu/assert";
-
-test("Math.sqrt()", () => {
-  assert.is(Math.sqrt(4), 2);
-  assert.is(Math.sqrt(144), 12);
-  assert.is(Math.sqrt(2), Math.SQRT2);
-});
-
-test("JSON", () => {
-  const input = {
-    foo: "hello",
-    bar: "world",
-  };
-
-  const output = JSON.stringify(input);
-
-  assert.snapshot(output, `{"foo":"hello","bar":"world"}`);
-  assert.equal(JSON.parse(output), input, "matches original");
-});
-
-test.run();
diff --git a/tests/diurnalAverage.test.js b/tests/diurnalAverage.test.js
new file mode 100644
index 0000000..1569d6f
--- /dev/null
+++ b/tests/diurnalAverage.test.js
@@ -0,0 +1,59 @@
+import { test } from "uvu";
+import * as assert from "uvu/assert";
+
+import moment from "moment-timezone";
+import { diurnalAverage } from "../index.js";
+
+// Start of Valentine's Day in Greenwich
+let start = moment.tz("2023-02-14 00:00:00", "UTC");
+let datetime = [];
+let x = [];
+
+// Precisely 10 days worth of data
+let day = 0;
+for (var i = 0; i < 240; i++) {
+  if (i % 24 === 0) day++;
+  datetime[i] = new Date(start + i * 3600 * 1000);
+  let val = 10 + 5 * Math.sin((i * Math.PI) / 12);
+  x[i] = Math.round(val * 10) / 10;
+}
+
+let hours = [
+  0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21,
+  22, 23,
+];
+
+test("diurnal averages work for 'UTC'", () => {
+  let timezone = "UTC";
+  let diurnal = diurnalAverage(datetime, x, timezone);
+  let averages = [
+    10, 11.3, 12.5, 13.5, 14.3, 14.8, 15, 14.8, 14.3, 13.5, 12.5, 11.3, 10, 8.7,
+    7.5, 6.5, 5.7, 5.2, 5, 5.2, 5.7, 6.5, 7.5, 8.7,
+  ];
+  assert.equal(diurnal.hour, hours);
+  assert.equal(diurnal.averages);
+});
+
+test("diurnal averages work for 'America/Chicago'", () => {
+  let timezone = "America/Chicago";
+  let diurnal = diurnalAverage(datetime, x, timezone);
+  let averages = [
+    15, 14.8, 14.3, 13.5, 12.5, 11.3, 10, 8.7, 7.5, 6.5, 5.7, 5.2, 5, 5.2, 5.7,
+    6.5, 7.5, 8.7, 10, 11.3, 12.5, 13.5, 14.3, 14.8,
+  ];
+  assert.equal(diurnal.hour, hours);
+  assert.equal(diurnal.averages);
+});
+
+// ----- Run all tests ---------------------------------------------------------
+
+test.run();
+
+// ----- Notes -----------------------------------------------------------------
+
+// Manual testing for "America/Chicago"
+
+// x.slice(0,24)
+// // (24) [10, 11.3, 12.5, 13.5, 14.3, 14.8, 15, 14.8, 14.3, 13.5, 12.5, 11.3, 10, 8.7, 7.5, 6.5, 5.7, 5.2, 5, 5.2, 5.7, 6.5, 7.5, 8.7]
+// x.slice(6,30)
+// // (24) [15, 14.8, 14.3, 13.5, 12.5, 11.3, 10, 8.7, 7.5, 6.5, 5.7, 5.2, 5, 5.2, 5.7, 6.5, 7.5, 8.7, 10, 11.3, 12.5, 13.5, 14.3, 14.8]
diff --git a/tests/interactive_tests.js b/tests/interactive_tests.js
index 4b2d999..c8f628d 100644
--- a/tests/interactive_tests.js
+++ b/tests/interactive_tests.js
@@ -29,20 +29,4 @@ let z = 1;
 
 // ----- PLAY AREA -------------------------------------------------------------
 
-let start = moment.tz("2023-02-14 00:00:00", "UTC");
-datetime = [];
-x = [];
-
-for (var i = 0; i < 240; i++) {
-  datetime[i] = new Date(start + i * 3600 * 1000);
-  let val = 10 + 5 * Math.sin((i * Math.PI) / 12) + Math.random() * 6 - 3;
-  x[i] = Math.round(val * 10) / 10;
-}
-
-for (var i = 0; i < 240; i++) {
-  datetime[i] = moment.tz(start + i * 3600 * 1000, "UTC");
-  let val = 10 + 5 * Math.sin((i * Math.PI) / 12) + Math.random() * 6 - 3;
-  x[i] = Math.round(val * 10) / 10;
-}
-
 let zzz = 1;
diff --git a/tests/nowcast.test.js b/tests/nowcast.test.js
new file mode 100644
index 0000000..5f62dce
--- /dev/null
+++ b/tests/nowcast.test.js
@@ -0,0 +1,21 @@
+import { test } from "uvu";
+import * as assert from "uvu/assert";
+
+import { pm_nowcast } from "../index.js";
+
+test("nowcast works properly", () => {
+  // Data from: https://forum.airnowtech.org/t/the-nowcast-for-pm2-5-and-pm10/172
+  // Answer should be 28.4 ug/m3 or 85 AQI
+  let pm25 = [34.9, 43, 50, 64.9, 69.2, 66.2, 53.7, 48.6, 49.2, 35, null, 21];
+  let nowcast = pm_nowcast(pm25);
+  assert.is(nowcast.length, pm25.length);
+  assert.is(nowcast[0], null);
+  assert.is(nowcast[11], 28.4);
+});
+
+test("nowcast handles missing values properly", () => {
+  let pm25 = [34.9, 43, 50, 64.9, 69.2, 66.2, 53.7, 48.6, 49.2, 35, null, null];
+  assert.is(pm_nowcast(pm25)[11], null);
+});
+
+test.run();
diff --git a/tests/trimDate.test.js b/tests/trimDate.test.js
index e766128..6af15ca 100644
--- a/tests/trimDate.test.js
+++ b/tests/trimDate.test.js
@@ -18,6 +18,19 @@ for (var i = 0; i < 240; i++) {
   x[i] = Math.round(val * 10) / 10;
 }
 
+test("trimming Date objects works for 'UTC'", () => {
+  let timezone = "UTC";
+  let trimmed = trimDate(datetime, x, timezone);
+  let tz_start = moment.tz(trimmed.datetime[0], timezone);
+  let tz_end = moment.tz(trimmed.datetime[239], timezone);
+  assert.is(trimmed.datetime.length, 240);
+  assert.is(tz_start.hours(), 0);
+  assert.is(tz_end.hours(), 23);
+  // UTC is 8 hours ahead of "America/Los_Angeles" during the winter
+  assert.is(trimmed.datetime[0].valueOf(), datetime[0].valueOf());
+  assert.is(trimmed.x[0], x[0]);
+});
+
 test("trimming Date objects works for 'America/Los_Angeles'", () => {
   let timezone = "America/Los_Angeles";
   let trimmed = trimDate(datetime, x, timezone);
@@ -28,6 +41,7 @@ test("trimming Date objects works for 'America/Los_Angeles'", () => {
   assert.is(tz_end.hours(), 23);
   // UTC is 8 hours ahead of "America/Los_Angeles" during the winter
   assert.is(trimmed.datetime[0].valueOf(), datetime[8].valueOf());
+  assert.is(trimmed.x[0], x[8]);
 });
 
 test("trimming Date objects works for 'America/New_York'", () => {
@@ -40,6 +54,7 @@ test("trimming Date objects works for 'America/New_York'", () => {
   assert.is(tz_end.hours(), 23);
   // UTC is 5 hours ahead of "America/New_York" during the winter
   assert.is(trimmed.datetime[0].valueOf(), datetime[5].valueOf());
+  assert.is(trimmed.x[0], x[5]);
 });
 
 // ----- Test passing in moment objects ----------------------------------------
@@ -61,6 +76,7 @@ test("trimming moment.tz objects works for 'America/Los_Angeles'", () => {
   assert.is(tz_end.hours(), 23);
   // UTC is 8 hours ahead of "America/Los_Angeles" during the winter
   assert.is(trimmed.datetime[0].valueOf(), datetime[8].valueOf());
+  assert.is(trimmed.x[0], x[8]);
 });
 
 test("trimming Date objects works for 'America/New_York'", () => {
@@ -73,6 +89,7 @@ test("trimming Date objects works for 'America/New_York'", () => {
   assert.is(tz_end.hours(), 23);
   // UTC is 5 hours ahead of "America/New_York" during the winter
   assert.is(trimmed.datetime[0].valueOf(), datetime[5].valueOf());
+  assert.is(trimmed.x[0], x[5]);
 });
 
 // ----- Run all tests ---------------------------------------------------------
diff --git a/trimDate.js b/trimDate.js
index 15e92e1..2c74720 100644
--- a/trimDate.js
+++ b/trimDate.js
@@ -19,7 +19,7 @@ export function trimDate(datetime, x, timezone) {
   let start = hours[0] === 0 ? 0 : 24 - hours[0];
   let end =
     hours[hours.length - 1] === 23
-      ? hours.length - 1
+      ? hours.length
       : hours.length - hours[hours.length - 1] - 1;
 
   let trimmed_datetime = datetime.slice(start, end);