The A1 and A1 mini bed is already factory trammed. However, sometime the tramming is not good an there is too much compensation to be made from the printer.
With this tool you can check if your bed is perfection trammed and or adjust the tramming
This is also perfect for the new A1 Bed
You can use an M3 screw and nut to keep the jauge in place.
The jauge is available on amazon