Troughton and Simms Everist Theodolite
The "Everist" theodolite was designed by Sir George Everest in about 1825 when he was home on sick leave from the Great Survey of India. The full vertical circle was not needed to read the shallow vertical angles in the survey from mountain top to mountain top.
I believe that this type of theodolite was also referred to as an explorers theodolite.
This theodolite is circa mid 1800's and is marked with a broad arrow and "WD 5411" .
I believe that the markings are related to "War Department" inspection number " 5411".
Unfortunately, I cannot find any information for War Department records that covers inspection numbers.
The level bubbles are missing along with a couple of reader magnifiers.
My estimate for the circa of this instrument ( 1855 - 1857 ) is possibly verified by the Wikipedia information below.
Wikipedia for The History of the British war Department reads as follows:
In 1794 the position of Secretary of State for War was created. The Secretary's department was at first unofficially known as the War Department. Colonial affairs were later added and it became the Colony Department. After the outbreak of war with revolutionary France it became Colony and War Department and on the restoration of peace in 1815 the Colonial Department. In February 1855 the offices of the Secretary of State for War, and Secretary at War were merged and the new department and became the War Department once again until in 1857 when it became the War Office. In 1964 the department became the Ministry of Defence.