# Timer 555 Calculator Pro vs SPL

The clearest difference is price: SPL at Free against Timer 555 Calculator Pro's $0.99. SPL also leads on update cadence (every 6 days vs every 3 months) and iOS requirement (9.3 vs 13.2). Timer 555 Calculator Pro's advantage is rating (4.7 vs 3.8) and in-app purchases (none vs 1). On review sentiment, ratings volume, ads and device support there is nothing between them.

SPL is free to download; Timer 555 Calculator Pro costs $0.99 up front. SPL sells 1 one-off in-app purchase. Timer 555 Calculator Pro asks for nothing beyond the download.

Timer 555 Calculator Pro holds the better App Store score, 4.7 against 3.8. Both are backed by a comparable volume of ratings — 3 and 4 respectively. Written reviews split almost evenly too, at 100% and 100% positive.

Timer 555 Calculator Pro ships an update every 3 months, SPL every 6 days. Both last shipped on October 23, 2026.

## The numbers

| Metric | Timer 555 Calculator Pro | SPL |
| --- | --- | --- |
| Price | $0.99 | **Free** |
| Rating | **[4.7 (3 ratings)](https://appshunter.io/ios/app/timer-555-calculator-pro/id833443125/reviews)** | [3.8 (4 ratings)](https://appshunter.io/ios/app/spl-12/id1549379598/reviews) |
| Number of ratings | 3 | **4** |
| Positive reviews | 100.0% of reviews | 100.0% of reviews |
| In-app purchases | **No** | Yes |
| Ads | No | No |
| Update frequency | Every 3 months | **Every 6 days** |
| Monetization | Paid | **Free with in-app purchases** |
| Size | 3 MB | 19 MB |
| Requires iOS | 13.2 | **9.3** |
| Devices | iPhone, iPad, iPod | iPhone, iPad, iPod |
| Age rating | 4+ | 4+ |
| Developer | [Siu Yuen Ho](https://appshunter.io/developer/814088527) | [Delta Seven Kft.](https://appshunter.io/developer/1355331300) |

## What reviewers say

### Timer 555 Calculator Pro

[App page](https://appshunter.io/ios/app/timer-555-calculator-pro/id833443125)

Calculate parameters for monostable and astable circuits. Find component combinations for desired pulse width or frequency. Share circuit files via iCloud Drive or AirDrop.

**Highlights:** Calculate monostable pulse width, Calculate astable frequency, Find component combinations, Adjust component tolerance, Unlimited combinations (Pro), Share circuit files

**In-app purchases:** none


### SPL

[App page](https://appshunter.io/ios/app/spl-12/id1549379598)

This utility app serves as a companion for the E-mu SP-12 drum machine, enabling users to save and load sequencer and sound memory data via MIDI. It includes a manual and sample banks for connection verification, with an upgrade option for custom sound loading.

**Highlights:** Save and load sequencer data, Save and load sound memory data, MIDI connection support, Built-in manual, Sample banks for connection verification, Upgrade for custom sound loading

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

**In-app purchases (1)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Full Functionality | $29.99 | one-time |


## Frequently asked questions

### Is Timer 555 Calculator Pro free?

Timer 555 Calculator Pro costs $0.99, with no in-app purchases.

### Is SPL free?

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

### Which has better reviews, Timer 555 Calculator Pro or SPL?

Timer 555 Calculator Pro is rated higher. Timer 555 Calculator Pro averages 4.7 out of 5 from 3 ratings, while SPL averages 3.8 from 4 ratings.

### Do Timer 555 Calculator Pro or SPL have ads?

Neither Timer 555 Calculator Pro nor SPL shows ads.

### Which is updated more often, Timer 555 Calculator Pro or SPL?

Timer 555 Calculator Pro ships an update every 3 months, and SPL every 6 days. Most recently, Timer 555 Calculator Pro was updated on October 23, 2026 and SPL on October 23, 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.*