1) Ruler, Yu chuk, Hwang jong chuk Yuchuk was used as a standard rule to investigate the measurement system of local administrator by an undercover emissary of the king in Chosun Dynasty. Hwang jong chuk, is also a kind of standard rule. Interestingly, the length of this rule was derived from a specific sound, that is wave length in modern language, and the weight of water corresponding to its volume was used as a standard of weight.   2) 2) Rain gauge, Cheuk woo ki. - This was developed in Chosun dynasty and the first one in the world. It is about 200 years ahead of Europe. This was used for the estimation of tax since production of rice is mostly depends on the rain. It was set up all over the regional area and the record of rainfall is still available. Its accuracy was found very reliable even in modern days.   3) Water Gauge, Su Pyo Created in 1749, the Chosun Dynasty, it was set up in the river to measure the level of water. The chuk, a unit of measuring length was engraved on both sides of the stone pillar from 1 chuk(21.5cm) to 10 chuk. The level of water less than 6 chuk means the water runs normal and stable, but more than 9 chuk, in danger of overflow. It was possible to expect a drought or an overflow on the basis of the level of water.   4) Sun dial, Angbuilgu This was the first public sun dial developed during the Chosun dynasty. There were 13 vertical lines indicating the different seasons. The principle lies in the fact that length of shadow changes depending on the altitude of the sun. There were also 7 horizontal lines and the position of shadow was used for the indication of time. The lines were engraved on the inside of hemisphere so that the shadow would be in sharp point always. The zero position of this sun dial was calibrated by a compass so that accurate time indication was possible.   5) Water Clock, Jakyungnu The literal meaning of Jakyungnu is a spontaneously-striking water clock. Devised first in 1434 and renewed in 1536, it measured time based on the change of water level. The principle is as follows: From a large brazen vessel located at the highest position, water flows to lower potter through a long waterspout. Leverage, which is touched by the measuring stick floating on the waterspout, rolls a small iron ball and this ball rings a bell. Gatekeepers, who keeps track of the number of times the bell rings, would beat a drum the same number of times to declare the time to the townspeople. It was used as a national standard clock at that time.