# ASHRAE Psychrometric Chart vs Duet Display

The clearest difference is price: Duet Display at Free against ASHRAE Psychrometric Chart's $19.99. Duet Display also leads on update cadence (every 3 weeks vs every 11 months) and review sentiment (45% vs 27%). ASHRAE Psychrometric Chart's advantage is in-app purchases (none vs 6) and ads (none vs shown). On iOS requirement there is nothing between them.

Duet Display is free to download; ASHRAE Psychrometric Chart costs $19.99 up front. Duet Display sells 6 in-app purchases, starting at $3.99 per month. ASHRAE Psychrometric Chart asks for nothing beyond the download.

ASHRAE Psychrometric Chart ships an update every 11 months, Duet Display every 3 weeks. The most recent releases landed on October 12, 2026 and October 31, 2026 respectively.

## The numbers

| Metric | ASHRAE Psychrometric Chart | Duet Display |
| --- | --- | --- |
| Price | $19.99 | **Free** |
| Rating | — | **[4.4 (49K ratings)](https://appshunter.io/ios/app/duet-display/id935754064/reviews)** |
| Number of ratings | — | **49K** |
| Positive reviews | 27.3% of reviews | **45.5% of reviews** |
| In-app purchases | **No** | Yes |
| Ads | **No** | Yes |
| Update frequency | Every 11 months | **Every 3 weeks** |
| Monetization | Paid | **Free with in-app purchases** |
| Size | 2 MB | 59 MB |
| Requires iOS | 13.0 | 13.0 |
| Devices | iPad | **iPhone, iPad, iPod, Vision Pro** |
| Age rating | 4+ | 4+ |
| Developer | [ASHRAE, Inc.](https://appshunter.io/developer/375374912) | [Duet, Inc.](https://appshunter.io/developer/935754063) |

## What reviewers say

### ASHRAE Psychrometric Chart

[App page](https://appshunter.io/ios/app/ashrae-psychrometric-chart/id584295008)

This interactive tool allows users to plot and customize psychrometric charts on their iPad. Easily create and save HVAC process graphs, update properties dynamically, and share charts and data via email. Supports both IP and SI units.

**Highlights:** Interactive psychrometric chart plotting, Customizable chart appearance, Dynamic property updates, Create and edit points and labels, Email charts and data, Unlimited projects and templates, Zoom and pinch functionality

**Features:** macOS Compatibility

**In-app purchases:** none


### Duet Display

[App page](https://appshunter.io/ios/app/duet-display/id935754064)

Transform your iPad or iPhone into an advanced, lag-free extra display for your Mac or PC. Interact with your computer using touch and gestures, and unlock professional drawing capabilities with Apple Pencil support.

**Highlights:** Extra display for Mac & PC, Lag-free performance, Touch and gesture support, Apple Pencil integration, Professional drawing tools, Portable productivity

**In-app purchases (6)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Duet Starter (Monthly) | $3.99 | per month |
| Duet Air (Monthly) | $5.99 | per month |
| Duet Pro | $7.99 | per month |
| Duet Starter (Annual) | $39.99 | per year |
| Duet Air (Annual) | $49.99 | per year |
| Duet Pro (Annual) | $79.99 | per year |

**What reviewers like**

- 🚀 Works seamlessly as a second screen
- 👍 Useful for productivity and multitasking
- 🎨 Great for artists and designers
- 💻 Extends desktop to iPad
- ⭐ Excellent customer support

**What reviewers complain about**

- 🐛 Connectivity issues and crashes
- 🔋 High battery consumption
- 🔒 Subscription model for full functionality
- 🔍 Confusing setup process
- 💸 Expensive for the features provided

**Reported bugs**

- Incompatibility with certain software and drivers
- Laggy performance and input delays
- Unreliable connection and frequent disconnects

**Requested features**

- Improved resolution and scaling options
- Better support for older devices and Windows
- More customization and control over settings
- Wireless connectivity without subscription


## Frequently asked questions

### Is ASHRAE Psychrometric Chart free?

ASHRAE Psychrometric Chart costs $19.99, with no in-app purchases.

### Is Duet Display free?

Duet Display is free to download, with in-app purchases available.

### Do ASHRAE Psychrometric Chart or Duet Display have ads?

Duet Display shows ads; ASHRAE Psychrometric Chart does not.

### Which is updated more often, ASHRAE Psychrometric Chart or Duet Display?

ASHRAE Psychrometric Chart ships an update every 11 months, and Duet Display every 3 weeks. Most recently, ASHRAE Psychrometric Chart was updated on October 12, 2026 and Duet Display on October 31, 2026.

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*Compared by [AppsHunter](https://appshunter.io/) from daily US App Store data. Review summaries are generated from verbatim App Store reviews.*