Well... In the early days, you would test your urine with a dipstick to see if there was glucose, which meant your glucose was elevated (it had a 1+, 2+, 3+ scale associated with the color of the dispstick). This was not very accurate and only really showed if your glucose was above ~ 180 mg/dl.
Then, in the 1980s there came out blood testing strips. You would prick your finger with a hideous looking device and put the drop on a strip. You would wait for the reaction to complete (like 60 seconds), then wipe off the strip and read the colors compared to a color chart on the strip bottle.
A short time later, some manufacturers released a "meter" that would read the color on the strip when it was inserted.
Then came the meters with strips that you actually applied the blood and got instant readings...