I am a Reading Intervention specialist and I ordered these timers to use with my groups. I noticed that the amount of sand differed from timer to timer. I called Lakeshore and the customer service person looked up comments on the product. Evidently they are calibrated even though the amount varies. The necks inside vary in width which explained it. I tested them after the phone call and they are 1 minute within a second or 2. That's fine with me! Thanks Lakeshore!

The 1 minute sand timers are great. I use them in class with my First Grade students when we practice our fluency and when we work on our rote math problems. They are strong and last the whole school year. My students also take the sand timers home to do their fluency homework!!!

I purchased a set of 1-Minute Sand Timers to use for "children's time" in church, as our pre-school and early elementary children practiced a listening prayer. One of them timed the prayer, and each of the children received one as a gift afterwards.