Birdathon vs Formula & Units
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
Birdathon
This app helps birdwatchers create and organize detailed checklists of their observations. It automatically records time and location, allowing for easy editing and customization. Users can visualize their sightings on maps, add field notes, and export data for sharing or further analysis.
- Observation-centric checklists
- Automatic time and location recording
- Customizable maps with boundary overlays
- Field notes for additional observations
- Multiple checklist sorting options
- Data export to CSV and other formats
- Create checklist templates
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Birdathon is an observation-centric tool for creating birding checklists. It helps you organize your checklists and share them with others. Use Birdathon in the field to quickly record whether and where a bird is seen or heard and the number observed. The time and location of each observation is automatically recorded. You can adjust the location, time entries and the count of birds observed at any time to ensure your records are accurate. You can add breeding codes to your observations. Checklist maps display the locations of your observations. You can overlay county boundaries for every US state. You can add a range circle such as a 5MR (5-mile Radius) to your maps. You can import and overlay custom kml/kmz files onto your maps. An Overview feature lets you see your combined observations for any time period, and displays a map showing any boundaries you have selected, so you can utilize the map feature even when you are not actively checklisting. You can export Overview data into a csv text file or create a new checklist template from the Overview. Your checklists can be viewed in taxonomic order, alphabetically, by rarity or as a timeline of species. You can enrich your checklist with field notes and add observations such as mammals, butterflies, wildflowers, etc., to make it a more complete record of your experience. You can organize your checklists into categories such as Day List, Year List, County List, Life List, etc., and assign color themes to your lists. Bird species may be added and deleted from your lists at any time. You can create new checklist templates from your previous lists or import templates created by others. You can change which template is being used. You can import text files into Birdathon, making them into templates or new checklists. Different export options for your checklists allow you to import into eBird or another copy of Birdathon. The bird species source data and other resources used in this app come from the following sources: AviList, a unified global checklist of birds, is the core data set used for Birdathon. https://www.avilist.org. Some data has been integrated from the following sources: The eBird/Clements checklist of birds of the world (https://www.birds.cornell.edu/clementschecklist/download/), the American Ornithological Society's (AOS) Checklist of North and Middle American Birds (https://checklist.americanornithology.org), and the American Birding Association's (ABA) checklist of North American Birds (https://www.aba.org/listing-taxonomy/) Alpha codes come from The Institute for Bird Populations’ Standardized 4- and 6-letter Bird Species Codes. https://www.birdpop.org/pages/birdSpeciesCodes.php. County boundary data is from the United States Geological Survey (USGS) TIGER/Line 2019 Shapefiles found on the United States Census Bureau's website at https://www.census.gov/geographies/mapping-files/time-series/geo/tiger-line-file.2019.html. Boundaries should be used as general guidelines and not be considered precise. Note especially where county boundaries follow creeks, rivers, ridge lines and other natural features, and so are of much finer resolution than can be shown on Birdathon’s maps. California breeding bird atlas blocks come from the California Bird Atlas, https://www.californiabirdatlas.org. California Bird Atlas logo and breeding code descriptions used with permission.
Formula & Units
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Formula & Units is an ultimate tool for calculation of complex scientific expressions and convertion of scientific units. Expressions may be comprised of variables and constants, possessing numeric values and sets of units. Support and info at www.volard.wordpress.com The application interface consists of three custom (A, B, C) value-units expressions and six preset constants, which may be added to the final expression field by pressing the corresponding buttons. Value-Units Expression contains three fields: value field, numerator (top) units field and denominator (bottom) units field. Units must be typed exactly as they appear in the provided list in the Help section. Power of unit is typed directly after unit : s2. Metric prefixes or unit prefixes are recognized automatically: mm = 1.0e-3 m, kA = 1000 A. Metric prefix micro- (1e-6), is changed to 'u'. Additional Units can be added upon request through www.volard.wordpress.com. Example of unit expression as it should appear in numerator or denominator fields: mm2*s*kg*uA-2*MPa-2. Upon addition or subtraction, unit expressions should be of the same dimensionality! Meters cannot be added to Pascals!!! Application provides set of widely used physico-chemical constants. Pressing the corresponding constant button adds the value to the final field. Presets are: Na - Avogadro's constant, h - Planck constant, F - Faraday constant, R - gas constant, kB - Boltzmann constant, g - acceleration of gravity, e - elementary charge, Pi - pi constant. (All in SI units) The final expression is a regular scientific formula consisting of value-units expressions, regular math operations, numbers and functions. Available math functions are provided with buttons-shortcuts. Dot is used as a decimal point. Pressing "Calculate" button evaluates final expression. By default, application converts all units to International System of Units (SI), but it is possible to set the required units directly to the final (where result is shown) units fields before calculation, then the result will be adjusted to meet the requirement. The resulting final expression can be copied to A expression field, by pressing a "A^" top bar button, for further conversion or calculations. For a simple conversion, type the expression that should be converted to A field and preferred units to the B field. Special attention should be paid to dimensionality! For example: To change m3 to US Gallon in expression s*kg/m3, type gal-1 to numerator field or gal to denominator field in the B expression. Press 'convert' button to get the final converted result. For conversion numeric value of B expression has no meaning. Examples can be found at www.volard.wordpress.com.
Screenshots
Verdict
The clearest difference is price: Birdathon at Free against Formula & Units's $3.99. Formula & Units's advantage is in-app purchases (none vs 4) and update cadence (every 2 months vs every 4 months). On ads, device support and iOS requirement there is nothing between them.
Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS
Birdathon is free to download; Formula & Units costs $3.99 up front. Birdathon sells 4 one-off in-app purchases. Formula & Units asks for nothing beyond the download.
Birdathon ships an update every 4 months, Formula & Units every 2 months. The most recent releases landed on October 24, 2026 and August 20, 2026 respectively.
| Parameter | Birdathon | Formula & Units |
|---|---|---|
| Price | Free — better | $3.99 |
| Rating | 4.7 (15 ratings) — better | — |
| Positive reviews | 100.0% of reviews | — |
| Number of ratings | 15 — better | — |
| Update frequency | Every 4 months | Every 2 months — better |
| Ads | No | No |
| In-app purchases | Yes | No — better |
| Monetization | Free | — |
| Devices | iPhone, iPad | iPhone, iPad |
| Requires iOS | 16.1 | 16.0 — better |
| Further details — not scored | ||
| Size | 192 MB | 1 MB |
| Age rating | 4+ | 4+ |
| Developer | Barry Langdon-Lassagne | Roman Volinsky |
In-app purchases
Birdathon
- Good Tip$0.99
- Great Tip$1.99
- Amazing Tip$2.99
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- Incredible Tip$4.99
Formula & Units
No in-app purchases








