Under many of my food storage containers of plastic, there are circles with numbers and an arrow in the middle pointing at one of the numbers. What does these symbols mean?
Could it be recycling information? Plastic type? Production date? Serial number? Suitable for a special type of food?
Here is a picture of a food storage container of plastic from IKEA:
(click for full size)
This is the date the item was manufactured. The upper dial gives the year, the middle one, the month.
The bottom indicator could be a mold identifier, and in some cases, it might be a shift indicator (although this would typically be a clock going from 1 to 3, 4, or 6 depending on how shifts are allocated rather than the example showing 0 to 5).
See e.g. this manufacturer's datasheet on mold indicators: http://www.plastixs.com/pdfs/datecodeti.pdf
Top to bottom: Year, Month, Week. See D-M-E injection mold components catalog p157. If a problem turns up, the date markers will allow the investgating team to run down the batch.
At our plastic company, the last dial is the material source identifier. We source the injection molding pellets for HDPE from different manfacturers of comparable quality to keep them hungry and to keep us from having a supply crisis. 1 = company 1's resin, 2 = company 2', etc. This way you can trace a quality issue to the date and material source. sometimes it is a shift and sometimes it is a day of the week, just depends on the company.
