# LWF Observer vs HydroCalc Basic

The clearest difference is in-app purchases: LWF Observer at none against HydroCalc Basic's 1. LWF Observer also leads on iOS requirement (13.0 vs 15.1). On price, update cadence, ads and device support there is nothing between them.

Both are free to download. HydroCalc Basic sells 1 one-off in-app purchase. LWF Observer asks for nothing beyond the download.

LWF Observer ships an update weekly, HydroCalc Basic every 11 days. The most recent releases landed on October 1, 2026 and October 4, 2026 respectively.

## The numbers

| Metric | LWF Observer | HydroCalc Basic |
| --- | --- | --- |
| Price | Free | Free |
| In-app purchases | **No** | Yes |
| Ads | No | No |
| Update frequency | **Weekly** | Every 11 days |
| Size | 35 MB | 35 MB |
| Requires iOS | **13.0** | 15.1 |
| Devices | iPhone, iPad, iPod | iPhone, iPad, iPod |
| Age rating | 4+ | 4+ |
| Developer | [LWF TECHNOLOGIES LTD](https://appshunter.io/developer/1713708772) | [Transparent Blue Water LLC](https://appshunter.io/developer/1847968351) |

## What reviewers say

### LWF Observer

[App page](https://appshunter.io/ios/app/lwf-observer/id6470452164)

**In-app purchases:** none


### HydroCalc Basic

[App page](https://appshunter.io/ios/app/hydrocalc-basic/id6752577110)

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

**In-app purchases (1)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Premium - Flow Units & Ad-Free | $1.99 | one-time |


## Frequently asked questions

### Is LWF Observer free?

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

### Is HydroCalc Basic free?

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

### Do LWF Observer or HydroCalc Basic have ads?

Neither LWF Observer nor HydroCalc Basic shows ads.

### Which is updated more often, LWF Observer or HydroCalc Basic?

LWF Observer ships an update weekly, and HydroCalc Basic every 11 days. Most recently, LWF Observer was updated on October 1, 2026 and HydroCalc Basic on October 4, 2026.

---

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