Assuming you are talking about WordClock …

Eclipse is shipped with W/C unterminated. There is an internal jumper (JP1101 on motherboard, just behind connector)  which can be used to add a 75 ohm terminator, but this is normally not installed.

Using an external terminator on a BNC-T is the best way to do it as it saves opening the box and is also  immediately visible.

Strange that the User Manual is mute on this topic !