# Quick mental calculation vs ZX81

The clearest difference is ads: ZX81 at none against Quick mental calculation's shown. ZX81 also leads on device support (4 vs 2). Quick mental calculation's advantage is iOS requirement (12.0 vs 15.0). On price, update cadence and in-app purchases there is nothing between them.

Both are free to download. Neither carries in-app purchases, so what you see is what you pay.

Quick mental calculation ships an update every 11 days, ZX81 every 10 days. The most recent releases landed on October 14, 2026 and October 22, 2026 respectively.

## The numbers

| Metric | Quick mental calculation | ZX81 |
| --- | --- | --- |
| Price | Free | Free |
| Rating | — | **[4.9 (92 ratings)](https://appshunter.io/ios/app/zx81/id1180117434/reviews)** |
| Number of ratings | — | **92** |
| Positive reviews | — | 98.4% of reviews |
| In-app purchases | No | No |
| Ads | Yes | **No** |
| Update frequency | Every 11 days | **Every 10 days** |
| Monetization | — | Free |
| Size | 21 MB | 86 MB |
| Requires iOS | **12.0** | 15.0 |
| Devices | iPhone, iPod | **iPhone, iPad, iPod, Apple Watch** |
| Age rating | 4+ | 9+ |
| Developer | [ERX](https://appshunter.io/developer/513941286) | [Kevin Palser](https://appshunter.io/developer/1180117433) |

## What reviewers say

### Quick mental calculation

[App page](https://appshunter.io/ios/app/quick-mental-calculation/id841970890)

**Features:** macOS Compatibility

**In-app purchases:** none


### ZX81

[App page](https://appshunter.io/ios/app/zx81/id1180117434)

Experience early 1980s home computing with this app dedicated to the Sinclair ZX80 and ZX81. It includes a wealth of example software, offering a nostalgic journey into the origins of personal computing.

**Highlights:** Sinclair ZX80/ZX81 emulation, Timex Sinclair 1000 support, Includes example software, Focuses on early 1980s computing, ROM code included with permission

**Features:** macOS Compatibility, Game Controller support, Apple Watch app, Vision Pro support

**In-app purchases:** none


## Frequently asked questions

### Is Quick mental calculation free?

Quick mental calculation is free to download, with no in-app purchases.

### Is ZX81 free?

ZX81 is free to download, with no in-app purchases.

### Do Quick mental calculation or ZX81 have ads?

Quick mental calculation shows ads; ZX81 does not.

### Which is updated more often, Quick mental calculation or ZX81?

Quick mental calculation ships an update every 11 days, and ZX81 every 10 days. Most recently, Quick mental calculation was updated on October 14, 2026 and ZX81 on October 22, 2026.

---

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