This is a standard vernier caliper with a fine adjustment feature. The basic design is fine but the fine adjustment feature is poorly designed/assembled. On the item received the slider was loose and tended to jam preventing free movement.
In order to make the caliper useable it was neccessary to dismantle the fine adjustment assembly and then reassemble to take out the slack. The result is a useable caliper but the fundamental flaw is the poor fit of the fine adjustment slider "a rattle fit" and the poor detail in the assembly of the screw adjuster which exacerbated this.
The caliper is now useable but required work to make it that way.