Glossary

Key terms used throughout the Arrivals Board documentation.

Flap: A single character cell on the board. Each flap displays one character and animates by splitting and flipping to reveal the next character, replicating the mechanical action of a physical split-flap display module.
Reel: The ordered sequence of characters available on a single flap. When a flap transitions from one character to another, it cycles through the characters on the reel in order --- just as a physical split-flap module rotates through its card stack. Arrivals offers three reel types: Unicode Modern, Lowercase, and PHL Station Strict.
Split-flap display: A mechanical display technology where each character position contains a set of flaps that rotate to show different characters. Split-flap displays were widely used in airports, train stations, and banks from the 1950s through the 1990s. Arrivals simulates this mechanism digitally.
Solari: Solari di Udine, the Italian company that manufactured the most iconic split-flap departure boards, found in airports and train stations worldwide. The name "Solari" is often used as a synonym for split-flap displays. Arrivals Board includes a PHL Station Strict reel type that replicates the look of original Solari hardware.
SSE (Server-Sent Events): A web technology that allows a server to push updates to a client over a persistent HTTP connection. Arrivals uses SSE to receive real-time posts from Mastodon-compatible instances. Unlike WebSockets, SSE is one-directional (server to client), which makes it simple and reliable for streaming timelines.
MQTT (Message Queuing Telemetry Transport): A lightweight messaging protocol designed for IoT devices and low-bandwidth networks. Arrivals subscribes to an MQTT topic on a broker and displays incoming messages on the board. MQTT is commonly used in home automation systems like Home Assistant and Node-RED. See MQTT.
OAuth: An open standard for authorization that allows Arrivals to access your social media accounts without storing your password. When you sign in to Mastodon, Bluesky, or Threads, you authorize Arrivals through the service's own sign-in page, and Arrivals receives a token that grants limited access to your account.
PKCE (Proof Key for Code Exchange): An extension to the OAuth 2.0 authorization flow that adds an extra layer of security. PKCE prevents authorization code interception attacks by using a dynamically generated cryptographic challenge. Arrivals uses PKCE for all OAuth flows. Pronounced "pixie."
App password: A dedicated, limited-scope password generated by a service (such as Bluesky) specifically for third-party app access. App passwords are used instead of your main account password, and can be revoked independently without changing your primary credentials.
Indicator lamp: A small colored light that appears next to a message on the board. Each source can set an indicator color to help you identify the origin or urgency of a message at a glance --- for example, red for alerts, green for social posts, blue for calendar events. Custom hex colors can be set via the API or Shortcuts.
Display override: A character shown on a flap that is not part of the standard reel alphabet. This includes emoji, accented characters, and lowercase letters (when using PHL Station Strict mode). The flap spins to the closest reel position, then displays the override character.
Lookahead window: The time range the Calendar source uses when deciding which events to display. For example, a 24-hour lookahead window means only events occurring within the next 24 hours appear on the board. Events beyond this window are ignored until they fall within range.
Deduplication: The process by which Arrivals detects and suppresses duplicate messages. If the same text arrives from multiple sources or is re-fetched during a poll cycle, Arrivals displays it only once. This prevents the board from showing the same message repeatedly.
CloudKit: Apple's cloud database and syncing framework. Arrivals uses CloudKit to sync settings, source configurations, and preferences across your devices via iCloud. When you configure a source on your iPad, CloudKit ensures that configuration appears on your Apple TV automatically.
WeatherKit: Apple's weather data framework, which provides current conditions, forecasts, and severe weather alerts. Arrivals uses WeatherKit to power the built-in Weather source. Weather data refreshes approximately every 15 minutes.
EventKit: Apple's framework for accessing calendar and reminder data on the device. Arrivals uses EventKit to read events from calendars on your device and display them on the board via the Calendar source. Calendar access requires explicit user permission.