Mr Tint is designed to allow printers to quickly print out a tint test chart on a digital printer to choose visually the ideal tint percentage for a color.
When designers choose a tint of a spot color, the often go by what they see on screen. However for traditional printing there is the concept of dot-gain (see https://en.wikipedia.org/wiki/Dot_gain), where an ink dot printed on paper will appear larger than expected because the ink dot bleeds out on the paper. This can vary by machine, paper type, ink type and dot size (Big dots bleed more, small dots don't bleed at all or can be too small to print) . The overall effect of this is the printed tint color will usually appear darker than expected, for example a 95% tint may look identical to a solid 100% color.
A common problem is where a designer will have a 100% color background and have a 90% tint of the color to simulate a water-mark effect. However when printed the effect vanishes or is too pronounced. The issue is design software must estimate how the tint will look on screen and assumes it will be printed on a traditional offset press with the expected dot-gain.
Digital printers handle a tint color differently. Digital printers only simulate tints using CMYK for example. The print driver or RIP calculates the tint color based on is several settings such as the color profile, the rendering intent, the type of input color and the type of substrate and printing process used. It does not know that the business card your client printed last week (that the client asked you to match to) was printed on an uncoated card. The end result is a digital print where the tint is too light or too dark.
Rather than guessing the correct color of tint, just use Mr Tint to quickly create a test chart and print it to the media, You can then select the tint to get the desired results you see on screen or match to a sample provided.