# O vs Hydraulic Training Calculators

The clearest difference is in-app purchases: O at none against Hydraulic Training Calculators's 2. O also leads on update cadence (every 6 weeks vs every 4 months). On price, ads, device support and iOS requirement there is nothing between them.

Both are free to download. Hydraulic Training Calculators sells 2 in-app purchases, starting at $9.49 per year. O asks for nothing beyond the download.

O ships an update every 6 weeks, Hydraulic Training Calculators every 4 months. The most recent releases landed on October 12, 2026 and October 15, 2026 respectively.

## The numbers

| Metric | O | Hydraulic Training Calculators |
| --- | --- | --- |
| Price | Free | Free |
| Rating | — | **[5.0 (1 ratings)](https://appshunter.io/ios/app/hydraulic-training-calculators/id1273715287/reviews)** |
| Number of ratings | — | **1** |
| In-app purchases | **No** | Yes |
| Ads | No | No |
| Update frequency | **Every 6 weeks** | Every 4 months |
| Monetization | — | Free with in-app purchases |
| Size | 40 MB | 16 MB |
| Requires iOS | **12.0** | 13.2 |
| Devices | iPhone, iPad, iPod | iPhone, iPad, iPod |
| Age rating | 4+ | 4+ |
| Developer | [HUTCHINSON](https://appshunter.io/developer/862345826) | [Gary Molton](https://appshunter.io/developer/1193080103) |

## What reviewers say

### O

[App page](https://appshunter.io/ios/app/o-ring/id1229032846)

**Features:** macOS Compatibility

**In-app purchases:** none


### Hydraulic Training Calculators

[App page](https://appshunter.io/ios/app/hydraulic-training-calculators/id1273715287)

This app offers a comprehensive suite of hydraulic and fluid power tools, including calculators for power, thermal balance, and pipework. It provides design guides, a symbol library, and unit converters. Users can access free interactive content and a trial of paid resources, with options for one-time unlocks or annual subscriptions for extensive training materials.

**Highlights:** Hydraulic calculators, Symbol library, Unit converter, Design guides, Troubleshooting fault finder, Training courses, Simulation experiments

**Features:** macOS Compatibility

**In-app purchases (2)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Annual Training Subscription | $9.49 | per year |
| Hydraulic Quiz Design Guides | $4.99 | one-time |


## Frequently asked questions

### Is O free?

O is free to download, with no in-app purchases.

### Is Hydraulic Training Calculators free?

Hydraulic Training Calculators is free to download, with in-app purchases available.

### Do O or Hydraulic Training Calculators have ads?

Neither O nor Hydraulic Training Calculators shows ads.

### Which is updated more often, O or Hydraulic Training Calculators?

O ships an update every 6 weeks, and Hydraulic Training Calculators every 4 months. Most recently, O was updated on October 12, 2026 and Hydraulic Training Calculators on October 15, 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.*