BLE - UUIDs of custom services

[s23]

Greetings

I am going through the BLE fundamentals course and I am doing exercise 1 of lesson 4, creating a custom service. From this exercise, creating the "LBS" service, a 128-BIT uuid is used. How is this actually determined?

In the lesson "Services and Characteristics", the 128-bit value is defined as something like 4A98-xxxx-1CC4-E7C1-C757-F1267DD021E8, while in the exercise, it's 

"0x00001524, 0x1212, 0xefde, 0x1523, 0x785feabcd123", for the button UUID. The UUIDs seem arbitrary.

[nordicator_prim3]

Custom UUIDs are arbitrary. So long as they don't share the base bluetooth UUID determined by SIG (the standard services) then it can be anything. The base UUID that you shouldn't use is XXXXXXXX-0000-1000-8000-00805F9B34FB.