Kinex Measuring Tools is a company in the Czech Republic that specializes in producing high precision measuring tools including squares, straight edges, gauge blocks, thread gauges, and other various metrology items.
We currently carry a selection of their squares and straight edges, which are made to a very high accuracy standard, yet are reasonably priced. While they aren't as fancy looking as some other squares, they are made of good quality materials and all production goes through a stringent QA process to verify that it meets the DIN 875 standard for accuracy.
These are the most accurate squares we carry. They are available in four levels of accuracy, as per DIN 875:
Level 2 - while the lowest accuracy level we carry, is still more accurate than boutique woodworking squares that are sold as high accuracy - we only carry this accuracy level for 45° miter style squares as it is a good compromise between price and accuracy for 45° angle measurement.
Level 1 - while the 2nd lowest accuracy level we carry, is still significantly more accurate than boutique woodworking squares that are sold as high accuracy.
Level 0 - squares made to this accuracy level are several times more accurate than typical high accuracy woodworking squares.
Level 00 - squares made to this accuracy level are about an order of magnitude more accurate than typical woodworking squares. While this sort of accuracy isn't really necessary for most woodworking tasks, it is great to have one or two of these on hand to check the accuracy of other squares, especially adjustable ones that can sometimes go out of calibration. Because these are so reasonably priced, squares made to this accuracy level are also a good choice for machine set up.