Last Updated: October 21, 2026
This policy covers one app: Which Formula, the Algebra 2 and trigonometry study aid that tells you which method a problem needs, on iPhone, iPad and Android. Our other apps are covered by the general Illumination Development privacy policy, which does not apply here. That policy describes accounts, reward balances and redemption records that this app does not have.
The short version
The app never sees your homework. There is no box to type a problem into, no camera scan and no sign-up. You answer questions about the shape of a problem by tapping, and the app points you at a method. Your drill scores and streak are saved on your phone and nowhere else.
What does leave the device is advertising, usage analytics and crash reports, plus a support message if you send one. Each is set out below with what it contains and how to limit it. The ads can be personalized, and we would rather say so up front.
What stays on the device
The app keeps one small store on the phone or tablet, for the Spot the method drill:
- for each method, how many times you picked it correctly and how many times you missed it (this is how practice rounds lean toward the ones you miss);
- your current daily streak and your best one;
- the date of the last daily set you finished, and its score.
The cheat sheet, the 39 methods and the questions that lead to them are built into the app, so it works offline and fetches no content from us. What you type into the cheat sheet search is used on the phone to filter the list and is not sent anywhere.
Delete my data, described below, erases the drill store. Deleting the app removes it too. If the device backs itself up to iCloud or to Google, that copy is governed by Apple's or Google's terms and your own backup settings, and we have no access to it.
What the app sends
None of what follows includes your name or email address, unless you type them into Contact support yourself.
An anonymous identifier
On first launch the app signs in anonymously to Google Firebase. That produces a random identifier for the installation. It is not a name, an email address or a phone number, and there is no password. It is attached to the installation's analytics and crash reports, and Contact support shows it to you as “User ID” so a message you send can be matched to crash reports from the same device. Nothing else is stored under it: the app keeps no records of its own on a server.
Usage analytics
The app reports a set of events to Google Analytics. They say which screen is open, how long the app took to start, and when an error message was shown. They also cover the Find my method questions you answered and the method you landed on, which cheat sheet topic or method page you opened, and when the privacy policy was opened. For the drill, each answer is reported as the method the problem belonged to and whether you got it right, and a finished round as its score. A cheat sheet search sends only how many letters you typed and how many results came back, never the words.
Google Analytics also collects its own app-instance identifier, coarse device information such as the model, operating system version and app version, and an approximate location that Google works out from the IP address. The app never asks for location permission. We use analytics to see which questions confuse people and which methods get missed, so the content can be fixed.
Crash and diagnostic reports
If the app crashes or hits a handled error, Google Crashlytics sends a report: the stack trace, the app version, the device model and operating system, and the anonymous identifier above. Analytics and crash reporting are both off in development builds.
Advertising
The app is free and carries banner advertising from Google AdMob and no one else. The banner sits on the home screen, the cheat sheet pages and the method pages. There is none on the Find my method questions and none in the drill. There are no full-screen or rewarded ads, and there is nothing to buy.
To serve an ad, the Google Mobile Ads SDK contacts Google and may collect device and advertising information. That means an advertising identifier (Google's advertising ID on Android, and Apple's Identifier for Advertisers on iPhone and iPad if you allow it), device signals, an approximate location derived from the IP address, and the request, impression and click themselves. We never see this identifier, and it is not connected to your drill scores.
Ads in this app can be personalized, where the law and your choices allow it. The app is not child-directed and does not ask Google to switch personalization off; the choices below are how you limit it. Google's use of what it collects is governed by Google's own privacy policy.
On iPhone and iPad: the tracking prompt
The app shows Apple's App Tracking Transparency prompt once, when it first opens. If you choose Ask App Not to Track, the app never receives Apple's Identifier for Advertisers and ads keep working without it. You can change your answer any time under iOS Settings → Privacy & Security → Tracking.
On Android: the advertising ID
The app asks for no runtime permission. The advertising-ID permission is present because the Google Mobile Ads SDK declares it, and it is used for advertising. You can reset or delete your advertising ID, or opt out of personalized ads, in your device's settings — on most phones, Settings → Privacy → Ads, or Settings → Google → Ads.
In the EEA, the UK and Switzerland
Where a consent regime applies, Google's consent message is shown before any ad is requested. It asks for your choices about personalized ads and about storing and reading information on the device, and Google's consent SDK keeps your answer on the device.
You can change your answer at any time: Settings → Ad privacy options reopens the same choices. That entry appears only where Google reports that a consent regime applies, so people elsewhere will not see it.
Contacting support
Settings → Contact support is the one place the app asks for anything about you. To send a message it needs your name, your email address, a topic and the message. Before you send, the form shows exactly what else goes with it under “Included with your message”: the app name and version, your device's platform and operating system version, and the anonymous identifier described above.
All of it arrives as an email in our support inbox, passed along by a small Google Apps Script service that exists only to forward it, with your address set as the reply-to. Your email address is used to answer you and for nothing else.
The form is optional. The app works fully without it, and if you never use it we never receive a name or an email address from you.
Delete my data
Settings → Delete my data does these things, right away and without asking us:
- It permanently erases the drill store on the device: the right and missed counts for every method, both streaks, and the last daily date and score. This works with no connection.
- It resets the Google Analytics identifiers held on the device, so later analytics start from a new app-instance identifier.
- It deletes the anonymous Firebase identifier described above and signs the app in again with a new, unrelated one. That step needs a connection. Offline, the drill store is still erased but the old identifier can survive; run Delete my data again once you are online to remove it.
Analytics events and crash reports already sent to Google are kept by Google under its own retention periods, keyed to identifiers that no longer lead back to this installation. If you want those looked at too, write to privacy@illuminationdevelopment.com.
Support messages you have already sent stay in our inbox, because a delivered email cannot be recalled. You can ask us to delete them at the same address.
What the app does not do
- No account, sign-up, username or profile.
- No place to type, photograph or upload a math problem, and no collection of your schoolwork.
- No rewards, no coins, no in-app purchases and nothing for sale.
- No chat, no shared content and no way to reach another person through the app.
- No location permission. The only location involved is the approximate one Google derives from the IP address, described above.
- No access to contacts, photos, files, camera, microphone, calendar or health data.
- No advertising network other than Google AdMob.
- We do not sell personal information. The advertising described above may count as sharing for cross-context behavioral advertising in the sense the CCPA and CPRA give that term; declining the tracking prompt, resetting or deleting your advertising ID, and opting out of personalized ads are how you limit it.
Children
Which Formula is a study aid for high school math, meant for students of 13 and over and for adults brushing up. It is not directed at children under 13, its advertising requests are not flagged as child-directed, and we do not knowingly collect personal information from anyone under 13. If you believe a child under 13 has sent us personal information through Contact support, write to privacy@illuminationdevelopment.com and we will delete it.
Languages
The app is in English and Spanish. This policy is in English, and it covers both.
Your rights
Under the GDPR, the UK GDPR, the CCPA and CPRA, and comparable laws elsewhere, you have rights to access, correct, port and delete the personal information a company holds about you. The only things this app gives us that name you are the name and email address in a support message you chose to send; everything else is keyed to a random identifier. You can erase what is on the device yourself with Delete my data, and ask us about anything else — a support message, or data Google already holds — by writing to privacy@illuminationdevelopment.com.
Information held by Google from serving ads, running analytics and receiving crash reports is subject to Google's privacy policy and the controls described above.
A note about this web page
The app does not display this page. Tapping Privacy Policy in Settings opens it in the device's browser, and this website uses Google Analytics to see which pages people find useful. That is described in the general policy, and it applies to your visit to this page, not to your use of the app.
Changes to this policy
If any of this stops being true, this page changes before the version that changes it reaches either store, and the App Store privacy label and Google Play Data safety form change with it. Revisions are posted here with an updated date.
Contact
Email: privacy@illuminationdevelopment.com
You can also reach us through our contact and support page.