Don't put your stylus directly on the platform of any digital gauge. That would indeed cause the problem you noted and also another. Many scales are magnetic and/or contain magnetic materials. The strong attraction would distort your measurement and might damage your cartridge
Does the AUDIO ADDITIVES - DIGITAL STYLUS FORCE GAUGE have a magnetic platform? Looks like the advertising
http://www.musicdirect.com/products/images.php?i=-1&p=31026&h=72700
shows it placed directly on the platform.