ive had mine for a long time now. its works great. its very accurate for being what it is. its within several tenths of your actual time, as long as you make multiple runs and average them out. its pointless to just use 1 time and take those measurements. **make sure its perfectly horizontal tho, its gotta be at 0.00 for it to be the most accurate. after u start tho, it will bounce up and down, but thats because your car is moving, so dont worry about that. and find out your weight, again, you gotta be as close to your actual to get the most accurate results.