I'm 43 and spent a very small amount of time at infants school using the imperial system before swapping to metric.  I can just about remember changing from metal weights for ounces to thin blue disks for grams.  I don't remember it being particularly confusing or anything.

Anyway, despite being brought up almost exclusively using the metric system, I still think in terms of imperial measurements.  I'm 5'11" and weigh 14 stone.

So, picture the scene.  We're putting the final touches to an e-commerce system where the postage rate is calculated according to weight.  To make the job quicker, I'm sat there adding weights to a few products to test and Claire is adding in the shipping rates.  For 1 unit in weight it's £3.50, for 2 units of weight it's £5.50.

So, I select 1 for the first product with lbs as the unit.  Claire adds the shipping weights and uses kgs.

We add one product to the cart and the shipping cost is £3.50.  Add another and it's still £3.50 when it should be £5.50.

It took us a while to work it out but we got there in the end!