This is handy when trying to date electronic equipment such as old synths. Gather together all the date codes from the chips and it will tell you that the unit was made some time after the latest date (not including any replacements of course). Often other components such as capacitors use the same format but it is less standard than on ICs. The date code will be either 3 digit, 4 digit (most common) or possibly a 4 digit with an additional letter on the start or end. Eg. 811, 8910, 8910A or A8910. There is a 2 digit type but as that can vary from manufacturer to manufacturer (and component) it is not covered here yet. For dating other components such as pots and speakers see my pot and speaker dating page.
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