I was 9 yrs old and part way through grade 4 when Canada switched from imperial measurements to the metric system. Having been taught both measurements in school I thought that it was just my generation that was "measurement bilingual", but I realize that my grown daughters also have this talent.
As Canadians we seem to switch from one measurement to the other with out any thought. For example, when I go to the fabric store I buy one meter of material and when I get home I sew a 5/8” seam which I trim to 1/4” and I don't even blink. If I was to make a trip to my local lumber yard I would drive 50 to 70 km and hour and once there I would buy 2x4's and 3/4” plywood.
It wasn't until I started writing crochet patterns that I even noticed. When I sat down to write my first pattern I figured that since I am Canadian I should write the pattern using Canadian spelling and measurements. This is what I was taught in school. So, I spell colour with a "u" (even though my word processor tells me I'm wrong), I use metric measurements and I crochet with metric hooks. This was all fine until I added sewing. I have never sewn anything other than a 5/8” seam and I have never heard it called anything else. My daughter had just finished a sewing course in school so I asked her what she was taught, and she also calls it a 5/8” seam. My other daughter was in wood works and she was using imperial measurements. This was when I first realized that in Canada we are still using both systems of measurements, hence the term “measurement bilingual”.
For a while I added both imperial and metric measurements to my patterns, but most of our customers were American and adding both measurements was tedious. I started adding both metric and US hook sizes, but I seem to own some crochet hooks that are oddly sized. For example 3.00 mm and 4.50 mm crochet hooks are missing from the US size charts. As hard as Tara and I were working to remain consistent we were running into problems.
In the end what does all of this mean? Well, although there may be slight variations on some of our older patterns we will do our best to include both metric and imperial measurements. However, a 5/8” seam will still be 5/8” seam and we may or may not spell colour with a "u", but for the most part we will do what we can to accommodate the needs of all our customers. In Canada when we buy a box a cereal the ingredients are written on the box in both English and French so it only makes sense that our crochet patterns should include both forms of measurements and hook sizes.