install-compute-machines.md

@@ -4,7 +4,7 @@ After physical installation, plug four 1G network connections into the first fou
 
 Next, create a PXE boot USB stick. This can be done with a USB stick of larger than 128Mb that allows you to write to it on the block level, using, for example, dd or UNetBootin. Write the provided iso file onto the USB stick. You will need one per compute node. Insert these PXE boot USB sticks into any USB socket on the compute machines.
 
-Now, Get the MAC address of the first port on each compute node, and update the database to include these values into the compute A and compute B serial number values. Compute A should be the one connected to Switch 2, and Compute B the one connected to Switch 3.
+Now, Get the MAC address of the first port on each compute node, and update the database to include these values into the compute A and compute B serial number values. The number consists of 12 positions and should start with 78d0042xxxxxx. Compute A should be the one connected to Switch 2, and Compute B the one connected to Switch 3.
 
 Lastly, boot the machines. They should automatically get their filesystem and begin processing.