A promise that a load stayed cold is worth nothing. A graph is worth arguing about, and the arguments are useful.
We put a logger in every chilled and frozen consignment, and hand the record over with the delivery note. Customers are usually pleased and then puzzled, because nobody has told them how to read one.
A logger records the temperature inside the box every few minutes. What you get is a line. The useful information is in the shape of it rather than the numbers at either end.
A good chilled run looks boring. The line starts at four or five degrees, wanders by a degree, and finishes where it started. That is a box that was pre chilled, packed full, opened once and delivered.
A line that starts at twelve and comes down is the commonest fault and it is not ours. It means the load was already warm when it was packed. A cold box does not chill anything: it slows down warming. Putting a warm load in a cold box gives you a cold surface and a middle that never got there, and the graph shows exactly that. This is why we will refuse a chilled load that has been standing, and it is the most unpopular thing we do.
A line with a sharp spike in the middle is a box that was opened, usually at a drop while somebody counted the contents in the sun. One spike of a few minutes is survivable. Four are not, and it is why we ask receivers to count inside rather than on the quay.
A line that climbs steadily from the start is a box with not enough gel or too much air in it. That is a packing decision and it is ours to fix.
And a flat line at exactly the right temperature for eleven hours with no variation at all is the one to be suspicious of. Loggers are cheap and some of them are not honest. We changed supplier in 2023 for that reason.
What to do with the record is the real question. Keep it. For medicines it should be filed for a year at both ends, and for food it settles an argument about who spoiled what before the argument becomes a relationship problem. We have paid for two loads we broke because the graph showed it was us, and we have declined one claim where the graph showed a load that was warm before we touched it. Both outcomes are better than the alternative, which is two people guessing.
If your current arrangement cannot tell you what temperature your medicine reached, that is not a small gap. It is the whole point of a cold chain.
