This is a cool little hourglass! I got it for homeschooling, time management, & the pomodoro technique (check out Jim Kwik). I bought a separate set of hourglass timers as well. I separately got a 30 sec, 1 min., 2 min., 3 min., 5 min., & 10 min. I tested them for accuracy & I got:30 sec- 32 sec /32 sec1 min- 58 sec /1:04 min2 min- 1:57 min /2:04 min3 min- 2:52 min /2:55 min5 min- 4:56 min /4:50 min10 min- 11:36 min /9:08 minThe second number is when I flipped it back over. Apparently they are different on each direction.20 minute timer: I tested this one & got 22 minutes, 20:42 seconds, & 20:39 seconds. The sand does stick to the sides a little (maybe static) & it takes a few seconds to go down after tapping. No big deal for me.For what I'm using them for, their accuracy is perfect. I don't need exact times, just close is great! I love that this timer is glass, with a plastic base (a wood base would be cooler, but I'm happy). I like that the purple color! It is just under 4" long. I like that the kids can see time pass. What 2 minutes, vs 5 minutes, vs 10 minutes, vs 20 minutes...etc. looks & feels like. I want to use my 20 minute hourglass for my daughter's school work, then 5 minutes of play or doing what she likes, & back & forth until the task is done. I've been using a normal kitchen timer for this, & it works great! But I love the hourglasses better! I will also be doing the same technique with my own work to do as well. I love that they don't make noise, don't take batteries, & you can watch them. I saw another review mentioned using them for sharing toys between siblings. I love that idea, I'm going to try that out. Our daughter is 7 & our son is 3 yrs in 2 months. I've flipped this timer about 10 times & it never sticks (which I've seen some reviews mention). The sand flows smooth. The same goes for the other timers I got. They all flow smooth & don't stick. Also, I love to read & am reading about 20 minutes each day so I love the 20 minute hourglass for that. Though I may use the 10 or even the 5 min. timer if I'm short on time or I want more than 20 minutes. Also for things like meditation, where a timer is very noisy & interrupting. Another thing is phone time & You Tube time for us adults. Also, episode watching for my daughter. I obviously know that I'll need to be paying attention & watching the timer for her TV time (until she eventually gets more responsible & gets used to it), but I'm ok with that. (TV isn't much of an issue in our house, as we are very outdoor oriented anyway.) I also see myself using these for any kind of time management for me, my kids or my family. I love these! I'm eventually going to purchase a 30 minute & an hour hourglass!