diff --git a/system/CONSTANTS.mjs b/system/CONSTANTS.mjs
index b34acb2..d839d23 100644
--- a/system/CONSTANTS.mjs
+++ b/system/CONSTANTS.mjs
@@ -1,14 +1,8 @@
+import { HELPERS } from "./helpers/HELPERS.mjs";
+
 export const SYSTEM_ID = "black-flag";
 export const SYSTEM_NAME = "Black Flag 🏴";
 
-function isDebugging() {
-  return game.modules.get("_dev-mode")?.api?.getPackageDebugValue(SYSTEM_ID);
-}
-
-function log(...args) {
-  if ( isDebugging() ) console.log(`${SYSTEM_NAME} |`, ...args);
-}
-
 /**
  * The expected distance units.
  * @type {{label: string}}
@@ -252,10 +246,9 @@ const CHARACTER_BUILDER_MODES = {
  * @type {Object}
  */
 export const SYSTEM = {
+  ...HELPERS,
   id: SYSTEM_ID,
   name: SYSTEM_NAME,
-  log,
-  isDebugging,
   TOOL_TYPES,
   SKILL_TYPES,
   PROFICIENCY_TYPES,
diff --git a/system/datamodels/item/common/duration.mjs b/system/datamodels/item/common/duration.mjs
new file mode 100644
index 0000000..ff8a3cc
--- /dev/null
+++ b/system/datamodels/item/common/duration.mjs
@@ -0,0 +1,34 @@
+/**
+ * Data model template for a Duration, as may be used by Powers
+ *
+ * @property {string} type
+ * @mixin
+ */
+export default class DurationDataModel extends foundry.abstract.DataModel {
+
+  /** @inheritdoc */
+  static _enableV10Validation = true;
+
+  /** @inheritDoc */
+  static defineSchema() {
+    const fields = foundry.data.fields;
+    return {
+      // Store duration internally as rounds, translating into human readable on the fly
+      rounds: new fields.NumberField({
+        required: false
+      }),
+
+      // Describes when during a round an effect might end
+      // e.g. "end of target's turn" or "end of caster's turn"
+      special: new fields.StringField({
+        required: false
+      }),
+
+      type: new fields.StringField({
+        required: true,
+        choices: ["instantaneous", "time", "permanent", "special"],
+        initial: "instantaneous"
+      })
+    };
+  }
+}
diff --git a/system/helpers/HELPERS.mjs b/system/helpers/HELPERS.mjs
new file mode 100644
index 0000000..75133d8
--- /dev/null
+++ b/system/helpers/HELPERS.mjs
@@ -0,0 +1,9 @@
+import {isDebugging, log} from "./debug.mjs";
+import {convertToRounds, formatRounds} from "./roundHelpers.mjs";
+
+export const HELPERS = {
+  convertToRounds,
+  formatRounds,
+  isDebugging,
+  log
+};
diff --git a/system/helpers/debug.mjs b/system/helpers/debug.mjs
new file mode 100644
index 0000000..148dc4e
--- /dev/null
+++ b/system/helpers/debug.mjs
@@ -0,0 +1,9 @@
+
+export function isDebugging() {
+  return game.modules.get("_dev-mode")?.api?.getPackageDebugValue(SYSTEM_ID);
+}
+
+export function log(...args) {
+  if ( isDebugging() ) console.log(`${SYSTEM_NAME} |`, ...args);
+}
+
diff --git a/system/helpers/roundHelpers.mjs b/system/helpers/roundHelpers.mjs
new file mode 100644
index 0000000..83b84d5
--- /dev/null
+++ b/system/helpers/roundHelpers.mjs
@@ -0,0 +1,87 @@
+/**
+ * Formats rounds for human readable display
+ *
+ * 1 round is nominally a "turn"
+ * 10 rounds is a minute
+ * 600 rounds is an hour
+ * 14400 rounds is a day
+ * 1008000 is a week
+ * 4032000 is a month
+ * 48384000 is a year
+ *
+ * @param {number} rounds
+ * @returns {{number: number, unit: string}}
+ */
+export function formatRounds(rounds) {
+  if (rounds < 10) {
+    return {
+      number: rounds,
+      unit: "turns"
+    };
+  }
+
+  if (rounds < 600) {
+    return {
+      number: Math.floor(rounds / 10),
+      unit: "minutes"
+    };
+  }
+
+  if (rounds < 14400) {
+    return {
+      number: Math.floor(rounds / 600),
+      unit: "hours"
+    };
+  }
+
+  if (rounds < 1008000) {
+    return {
+      number: Math.floor(rounds / 14400),
+      unit: "days"
+    };
+  }
+
+  if (rounds < 4032000) {
+    return {
+      number: Math.floor(rounds / 1008000),
+      unit: "weeks"
+    };
+  }
+
+  if (rounds < 48384000) {
+    return {
+      number: Math.floor(rounds / 4032000),
+      unit: "months"
+    };
+  }
+
+  return {
+    number: Math.floor(rounds / 48384000),
+    unit: "years"
+  };
+}
+
+/**
+ * Converts an object of number and unit into a number of rounds
+ * @param {number} number
+ * @param {string} unit
+ * @returns {number} - a number of rounds
+ */
+export function convertToRounds(number, unit) {
+  switch (unit) {
+    case "turns":
+      return number;
+    case "minutes":
+      return number * 10;
+    case "hours":
+      return number * 600;
+    case "days":
+      return number * 14400;
+    case "weeks":
+      return number * 1008000;
+    case "months":
+      return number * 4032000;
+    case "years":
+      return number * 48384000;
+  }
+}