Both the UG-1 Imperial and Metric versions have a metric centering rule. The centering rule on the UG-1 can be used to quickly find dead center of stock up to 140mm(5.5") in width. The scale is metric which is ideal for a centering rule because all you need to do is align the two same numbers on the right and the left of the stock, and the rule will indicate center at the 0 mark.
On the UG-1 Imperial, the marking gauge and the depth gauge would be in inches with the marking gauge having both metric and imperial on each side for easier conversions if needed. The metric version would only have mm on the left side of the marking gauge and is blank on the right side and has the depth gauge in metric as well without any inch graduations. Please see below photos of both the UG-1 Imperial and UG-1 Metric for a visual comparison.