Accurate travel time don't worry about the time being inaccurate. These practice learning kits have high performance-price suitable for bulk purchase of school and educational institution. Manufacturered by Gikfun. Supply voltage: 3V ~ 6V PCB Size: 50mm x 19mm. Please make sure all components in right direction and right place; and check whether pseudo and float welding this is very important in practicing and testing. This practical practice board is easy to assemble and soldering exactly suitable for the electronic learner and school teaching.