Android OS v6 and newer requires Location Permission to use Bluetooth.
Location permission is required when using Go Direct sensors connected via Bluetooth.
Vernier Apps do not collect, transmit, or store location information.

Any use of Bluetooth to scan for devices by an application requires the user grant permission to use location information when running Android 6.0 and newer. If permission is denied, our apps will be unable to communicate with Go Direct devices via Bluetooth.

Turning on the Location Permission

When a Vernier app is first launched, you will be asked to grant permissions. If at that time you elect not to allow the location permission, setting the permission must be done manually. This is done in two places.

1. Location Permission for Your Device
   1. Swipe down from the top of the screen and tap the gear icon to access the Settings app.
   2. Under Security & Location, tap Location and make sure it is turned on.

2. App Permission to use Location
   1. Go back to the Settings app and select Apps & Notifications
   2. Tap App Permissions then select Location.
   3. Find your app in the list (e.g., Graphical Analysis), then turn on the permission.
      If presented with options for Access Level, we recommend Allow only while using the app.

Exact names for the Settings app options vary depending on the version of Android OS you are running.

Alternative Method
You can always uninstall and then reinstall the app. This will restore the dialog that asks at launch if you want to give location permissions to the app.

Related Link
● Graphical Analysis, Instrumental Analysis, or Spectral Analysis says that Bluetooth is off, but I am sure it is on. (Android devices)