Ever since the very beginning of railway traffic, one of the foremost tasks has been to ensure traffic safety. Staff instruments was one of the first devices to serve this purpose and help control traffic between at least two stations. Their introduction in Latvia began in 1922, as it gradually replaced communication via telegraph and telephone.

Staff instruments at two neighbouring stations were interlocked so that only one staff providing permission to enter a certain section could be removed at a time; without it, the locomotive driver was not permitted to enter the section. Each staff was marked with a number, batch and station names between which it was used. The staff was valid only within the section specified on it. The staff instrument was operated by the station master only, who used a mechanical staff exchanger or handed it to the locomotive driver manually by stepping out on the platform.

In 1925, the manufacture of staff instruments began in the workshops of Latvian railways; and in 1927, electrotechnical workshops took over. In 1938, 288 staff instruments were operated on Latvian railways. In the 1935th saw the construction of staff instruments for traffic control systems in Latvia, which were used on less important lines when train traffic control came under the charge of a single dispatcher.

Today, the only railway section in Latvia to employ this kind of system is Zasulauks-Bolderāja in Riga.