# Doppler Effect Calculator vs Modbus TCP Station

The clearest difference is price: Modbus TCP Station at Free against Doppler Effect Calculator's $2.99. Modbus TCP Station also leads on update cadence (every 10 days vs every 26 months) and iOS requirement (15.0 vs 17.6). Doppler Effect Calculator's advantage is in-app purchases (none vs 2) and ads (none vs shown). On device support there is nothing between them.

Modbus TCP Station is free to download; Doppler Effect Calculator costs $2.99 up front. Modbus TCP Station sells 2 one-off in-app purchases. Doppler Effect Calculator asks for nothing beyond the download.

Doppler Effect Calculator ships an update every 26 months, Modbus TCP Station every 10 days. The most recent releases landed on October 8, 2026 and October 24, 2026 respectively.

## The numbers

| Metric | Doppler Effect Calculator | Modbus TCP Station |
| --- | --- | --- |
| Price | $2.99 | **Free** |
| Rating | **[5.0 (1 ratings)](https://appshunter.io/ios/app/doppler-effect-calculator/id1410084954/reviews)** | — |
| Number of ratings | **1** | — |
| Positive reviews | 0.0% of reviews | — |
| In-app purchases | **No** | Yes |
| Ads | **No** | Yes |
| Update frequency | Every 26 months | **Every 10 days** |
| Monetization | Paid | — |
| Size | 1 MB | 31 MB |
| Requires iOS | 17.6 | **15.0** |
| Devices | iPhone, iPad | **iPhone, iPad, iPod** |
| Age rating | 4+ | 4+ |
| Developer | [Nitrio](https://appshunter.io/developer/321121189) | [DONGSOO LEE](https://appshunter.io/developer/1868670088) |

## What reviewers say

### Doppler Effect Calculator

[App page](https://appshunter.io/ios/app/doppler-effect-calculator/id1410084954)

This physics and math calculator helps determine the frequency of sound waves when the source or observer is in motion. It provides instant calculations with copyable results and includes reference formulas. The app supports various units and high precision, working seamlessly on iOS devices.

**Highlights:** Instant calculations, Copyable results, Reference formulas included, Supports 16 decimal places, Multiple unit support, Ad-free and private

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases:** none


### Modbus TCP Station

[App page](https://appshunter.io/ios/app/modbus-tcp-station/id6757790321)

**Features:** macOS Compatibility

**In-app purchases (2)**

| Purchase | Price | Billing |
| --- | --- | --- |
| 1-Month Premium Pass | $0.99 | one-time |
| Premium Upgrade | $9.99 | one-time |


## Frequently asked questions

### Is Doppler Effect Calculator free?

Doppler Effect Calculator costs $2.99, with no in-app purchases.

### Is Modbus TCP Station free?

Modbus TCP Station is free to download, with in-app purchases available.

### Do Doppler Effect Calculator or Modbus TCP Station have ads?

Modbus TCP Station shows ads; Doppler Effect Calculator does not.

### Which is updated more often, Doppler Effect Calculator or Modbus TCP Station?

Doppler Effect Calculator ships an update every 26 months, and Modbus TCP Station every 10 days. Most recently, Doppler Effect Calculator was updated on October 8, 2026 and Modbus TCP Station on October 24, 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.*