# PreFresh Pen Size Calculator vs HERD SD

The clearest difference is update cadence: HERD SD at every 2 days against PreFresh Pen Size Calculator's every 16 months. PreFresh Pen Size Calculator's advantage is iOS requirement (12.0 vs 14.0). On price, ads, in-app purchases and device support there is nothing between them.

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

PreFresh Pen Size Calculator ships an update every 16 months, HERD SD every 2 days. The most recent releases landed on November 1, 2026 and September 30, 2026 respectively.

## The numbers

| Metric | PreFresh Pen Size Calculator | HERD SD |
| --- | --- | --- |
| Price | Free | Free |
| In-app purchases | No | No |
| Ads | No | No |
| Update frequency | Every 16 months | **Every 2 days** |
| Size | 6 MB | 33 MB |
| Requires iOS | **12.0** | 14.0 |
| Devices | iPhone, iPad, iPod | iPhone, iPad, iPod |
| Age rating | 4+ | 4+ |
| Developer | [University of Wisconsin - Madison School of Veterinary Medicine](https://appshunter.io/developer/871872159) | [Grazielle Cioletti](https://appshunter.io/developer/1825411960) |

## What reviewers say

### PreFresh Pen Size Calculator

[App page](https://appshunter.io/ios/app/prefresh-pen-size-calculator/id983609290)

**Features:** macOS Compatibility

**In-app purchases:** none


### HERD SD

[App page](https://appshunter.io/ios/app/herd-sd/id6748356498)

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

**In-app purchases:** none


## Frequently asked questions

### Is PreFresh Pen Size Calculator free?

PreFresh Pen Size Calculator is free to download, with no in-app purchases.

### Is HERD SD free?

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

### Do PreFresh Pen Size Calculator or HERD SD have ads?

Neither PreFresh Pen Size Calculator nor HERD SD shows ads.

### Which is updated more often, PreFresh Pen Size Calculator or HERD SD?

PreFresh Pen Size Calculator ships an update every 16 months, and HERD SD every 2 days. Most recently, PreFresh Pen Size Calculator was updated on November 1, 2026 and HERD SD on September 30, 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.*