# Timer 555 Calculator vs Operational Amplifiers Guide

The clearest difference is in-app purchases: Operational Amplifiers Guide at none against Timer 555 Calculator's 1. Timer 555 Calculator's advantage is ads (none vs shown) and iOS requirement (13.2 vs 16.0). On price, update cadence and device support there is nothing between them.

Both are free to download. Timer 555 Calculator sells 1 one-off in-app purchase. Operational Amplifiers Guide asks for nothing beyond the download.

Timer 555 Calculator ships an update every 3 months, Operational Amplifiers Guide every 2 months. The most recent releases landed on September 24, 2026 and September 19, 2026 respectively.

## The numbers

| Metric | Timer 555 Calculator | Operational Amplifiers Guide |
| --- | --- | --- |
| Price | Free | Free |
| Rating | **[3.9 (8 ratings)](https://appshunter.io/ios/app/timer-555-calculator/id834044557/reviews)** | — |
| Number of ratings | **8** | — |
| Positive reviews | 100.0% of reviews | — |
| In-app purchases | Yes | **No** |
| Ads | **No** | Yes |
| Update frequency | Every 3 months | **Every 2 months** |
| Monetization | Free with in-app purchases | — |
| Size | 3 MB | 17 MB |
| Requires iOS | **13.2** | 16.0 |
| Devices | **iPhone, iPad, iPod** | iPhone, iPad |
| Age rating | 4+ | 4+ |
| Developer | [Siu Yuen Ho](https://appshunter.io/developer/814088527) | [ALG Software Lab](https://appshunter.io/developer/1650561236) |

## What reviewers say

### Timer 555 Calculator

[App page](https://appshunter.io/ios/app/timer-555-calculator/id834044557)

Calculate monostable and astable circuits for electronics projects. Determine pulse width and frequency, find component combinations, and save/upload data. Supports multiple languages.

**Highlights:** Monostable circuit pulse width calculation, Astable circuit frequency calculation, Component combination finder, Save component values to CSV, Upload CSV via AirDrop/iCloud Drive, Multi-language support

**Features:** Vision Pro support

**In-app purchases (1)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Unlock Pro feature | $0.99 | one-time |


### Operational Amplifiers Guide

[App page](https://appshunter.io/ios/app/operational-amplifiers-guide/id6467499897)

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

**In-app purchases:** none


## Frequently asked questions

### Is Timer 555 Calculator free?

Timer 555 Calculator is free to download, with in-app purchases available.

### Is Operational Amplifiers Guide free?

Operational Amplifiers Guide is free to download, with no in-app purchases.

### Do Timer 555 Calculator or Operational Amplifiers Guide have ads?

Operational Amplifiers Guide shows ads; Timer 555 Calculator does not.

### Which is updated more often, Timer 555 Calculator or Operational Amplifiers Guide?

Timer 555 Calculator ships an update every 3 months, and Operational Amplifiers Guide every 2 months. Most recently, Timer 555 Calculator was updated on September 24, 2026 and Operational Amplifiers Guide on September 19, 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.*