user: You are a structured reasoning expert tasked with solving problems step by step. 
You first think about the reasoning process in the mind and then provide the answer. The reasoning process and answer should be enclosed within <think> </think> and <answer> </answer> tags, respectively, i.e., <think> reasoning process here </think> <answer> answer here </answer>. 
Given a question and the associated knowledge graph triplets (entity, relation, entity), you are asked to answer the question with these triplets and your own knowledge. 
You can break down the original question into several sub-questions and explore the given knowledge graph to solve them step-by-step. If there are multiple possible answers, choose one as the final answer. 
After thinking, when you finally reach a conclusion, clearly state the answer within <answer> </answer> tags, i.e., <answer> answer here </answer>. 
Question: seismometer is the subclass of what measuring instrument? 
Knowledge Triplets: John Milne, people.deceased_person.place_of_death, Shide, Isle of Wight
In June 1895, he settled in Shide Hill House on the Isle of Wight, where he set up a laboratory., base.kwebbase.kwsentence.kwtopic, John Milne
John Milne, people.person.place_of_birth, Liverpool
Lochgelly, location.location.people_born_here, Thomas Lomar Gray
m.0bq_cmg, dataworld.gardening_hint.replaced_by, James Alfred Ewing
OBS: Ocean Bottom Seismometer, measurement_unit.measuring_instrument.subclass_of, Seismometer
Educator, people.profession.people_with_this_profession, Thomas Lomar Gray
John Milne, base.kwebbase.kwtopic.connections_from, john milne member of royal society
Luigi Palmieri, people.person.profession, Meteorologist
Zhang Heng, people.person.profession, Engineer
Milne's seismograph was simple enough to be installed on a global basis., base.kwebbase.kwsentence.kwtopic, John Milne
John Milne, people.deceased_person.date_of_death, 1913-07-31
John Milne, base.kwebbase.kwtopic.has_sentences, Eventually, the chain numbered forty observatories, carrying out continuous seismic surveillance in a global network.
prince boris borisovich golitsyn built on work of john milne, base.kwebbase.kwconnection.other, John Milne
john milne member of royal society, base.kwebbase.kwconnection.subject, John Milne
Seismometer, base.schemastaging.context_name.pronunciation, g.125_ppgnk
Zhang Heng, people.person.profession, Mathematician
Luigi Palmieri, people.deceased_person.place_of_death, Naples
Philosopher, people.profession.people_with_this_profession, Zhang Heng
Magnetic induction in iron and other metals, book.written_work.author, James Alfred Ewing
The strength of materials, book.written_work.author, James Alfred Ewing
Scientist, people.profession.people_with_this_profession, Thomas Lomar Gray
John Milne, book.author.works_written, A catalogue of destructive earthquakes
John Milne, base.kwebbase.kwtopic.category, unknown
Zhang Heng, user.lindenb.default_domain.scientist.known_for, Armillary sphere
James Alfred Ewing, book.author.works_written, The strength of materials
Despite being awarded the Order of the Rising Sun by the Japanese Emperor, Milne resigned from the Imperial University., base.kwebbase.kwsentence.kwtopic, John Milne
Faicchio, location.location.people_born_here, Luigi Palmieri
John Milne, base.kwebbase.kwtopic.has_sentences, In England he worked in mines in Cornwall and Lancashire.
m.0qyz3p9, dataworld.gardening_hint.last_referenced_by, Seismometer
m.03lfd2q, people.place_lived.person, Zhang Heng
John Milne, book.author.works_written, Earthquakes and Other Earth Movements
Luigi Palmieri, people.person.place_of_birth, Faicchio
Zhang Heng, user.lindenb.default_domain.scientist.known_for, Approximations of π
Zhang Heng, people.person.profession, Politician
Zhang Heng, user.avh.default_domain.ellerdale_topic.ellerdale_id, 009a-a093
John Milne, base.kwebbase.kwtopic.has_sentences, Milne's seismograph was simple enough to be installed on a global basis.
He then went to Freiburg in Germany, where he studied mineralogy from 1872 to 1873., base.kwebbase.kwsentence.kwtopic, John Milne
Milne was able to detect different types of earthquake waves,  and estimate wave velocities., base.kwebbase.kwsentence.kwtopic, John Milne
Seismological observations and earth physics, book.written_work.author, John Milne
Zhang Heng, base.schemastaging.context_name.pronunciation, g.125_ryr2s
Nanyang, location.location.people_born_here, Zhang Heng
Astronomer, people.profession.people_with_this_profession, Zhang Heng
Educator, people.profession.people_with_this_profession, John Milne
James Alfred Ewing, people.person.profession, Engineer
James Alfred Ewing, people.person.gender, Male
Thomas Lomar Gray, law.inventor.inventions, Seismometer
m.019h, type.permission.controls, m.0qyz3p9
James Alfred Ewing, people.deceased_person.date_of_death, 1935-01-07
James Alfred Ewing, people.deceased_person.place_of_burial, Ascension Parish Burial Ground
Engineer, people.profession.people_with_this_profession, John Milne
m.04hsl4n, people.place_lived.person, John Milne
Mathematician, people.profession.people_with_this_profession, Zhang Heng
Zhang Heng, user.lindenb.default_domain.scientist.known_for, Seismometer
Zhang Heng, people.deceased_person.place_of_death, Luoyang
Thomas Lomar Gray, people.deceased_person.date_of_death, 1908-12-19
Seismometer, law.invention.inventor, John Milne
John Milne, base.kwebbase.kwtopic.connections_to, prince boris borisovich golitsyn built on work of john milne
m.010qr31v, dataworld.gardening_hint.last_referenced_by, Luigi Palmieri
Thomas Lomar Gray, people.person.gender, Male
m.0tbt8dd, dataworld.gardening_hint.last_referenced_by, m.0qyz3p9
Mechanical Engineer, people.profession.people_with_this_profession, Zhang Heng
John Milne, base.kwebbase.kwtopic.has_sentences, Milne talked the Royal Society into financing a chain of earthquake observatories around the world, all equipped with his seismographs.
John Milne, base.kwebbase.kwtopic.kwtype, Person
Seismometer, measurement_unit.measuring_instrument.subclasses, OSS: Ocean Subbottom Seismometer
Seismometer, law.invention.inventor, Luigi Palmieri
Luigi Palmieri, people.person.date_of_birth, 1807-04-22
Seismometer, law.invention.inventor, James Alfred Ewing
John Milne, people.person.education, m.0n0y03_
John Milne, base.kwebbase.kwtopic.disciplines, seismology
Zhang Heng, symbols.name_source.namesakes, Chang Heng
m.04q69wz, people.place_lived.person, Zhang Heng
Dundee, location.location.people_born_here, James Alfred Ewing
Thomas Lomar Gray, people.person.profession, Scientist
m.0n0y03_, education.education.student, John Milne
Luigi Palmieri, people.deceased_person.date_of_death, 1896-09-09
Liverpool, location.location.people_born_here, John Milne
Luigi Palmieri, law.inventor.inventions, Seismometer
OSS: Ocean Subbottom Seismometer, measurement_unit.measuring_instrument.subclass_of, Seismometer
Zhang Heng, people.person.religion, Confucianism
John Milne, organization.organization_founder.organizations_founded, Seismological Society of Japan
Seismometer, measurement_unit.measuring_instrument.subclass_of, OSS: Ocean Subbottom Seismometer
Zhang Heng, people.person.profession, Philosopher
Thomas Lomar Gray, people.person.nationality, United Kingdom
Zhang Heng, people.person.profession, Scientist
Milne talked the Royal Society into financing a chain of earthquake observatories around the world, all equipped with his seismographs., base.kwebbase.kwsentence.kwtopic, John Milne
Seismometer, law.invention.inventor, Thomas Lomar Gray
Zhang Heng, people.person.place_of_birth, Nanyang
Thomas Lomar Gray, people.person.profession, Educator
James Alfred Ewing, book.author.works_written, Magnetic induction in iron and other metals
Zhang Heng, user.lindenb.default_domain.scientist.known_for, Lunar eclipse
m.0tqzmqt, dataworld.gardening_hint.last_referenced_by, Zhang Heng
m.04hvq5f, education.education.student, James Alfred Ewing
John Milne, people.person.profession, Engineer
In England he worked in mines in Cornwall and Lancashire., base.kwebbase.kwsentence.kwtopic, John Milne
John Milne, base.kwebbase.kwtopic.has_sentences, In Japan, he began a comprehensive study of volcanoes and earthquakes.
Thomas Lomar Gray, people.person.education, m.02wmymg
Thomas Lomar Gray, people.person.place_of_birth, Lochgelly
Geologist, people.profession.people_with_this_profession, John Milne
Later in 1873, he went to Canada, visiting  Newfoundland and Labrador to study the mineral resources there., base.kwebbase.kwsentence.kwtopic, John Milne
John Milne, law.inventor.inventions, Seismometer
John Milne was possibly the greatest individual contributor to observational earthquake investigations and the field of seismology., base.kwebbase.kwsentence.kwtopic, John Milne
Chang Heng, symbols.namesake.named_after, Zhang Heng
Engineer, people.profession.people_with_this_profession, Zhang Heng
John Milne, base.kwebbase.kwtopic.has_sentences, In June 1895, he settled in Shide Hill House on the Isle of Wight, where he set up a laboratory.
Scottish people, people.ethnicity.people, James Alfred Ewing
James Alfred Ewing, law.inventor.inventions, Seismometer
John Milne, book.author.works_written, Seismological observations and earth physics
John Milne, base.kwebbase.kwtopic.has_sentences, Despite being awarded the Order of the Rising Sun by the Japanese Emperor, Milne resigned from the Imperial University.
Engineer, people.profession.people_with_this_profession, James Alfred Ewing
Meteorologist, people.profession.people_with_this_profession, Luigi Palmieri
Thomas Lomar Gray, people.person.date_of_birth, 1850-02-04
James Alfred Ewing, people.person.place_of_birth, Dundee
James Alfred Ewing, people.person.ethnicity, Scottish people
1802 Zhang Heng, symbols.namesake.named_after, Zhang Heng
Zhang Heng, people.person.profession, Writer
Luigi Palmieri, people.person.gender, Male
m.0sw314b, education.education.student, Luigi Palmieri
Zhang Heng, people.person.nationality, China
Zhang Heng, people.person.gender, Male
James Alfred Ewing, people.person.education, m.04hvq5f
Seismometer, measurement_unit.measuring_instrument.subclasses, OBS: Ocean Bottom Seismometer
John Milne, base.kwebbase.kwtopic.has_sentences, He then went to Freiburg in Germany, where he studied mineralogy from 1872 to 1873.
Luigi Palmieri, people.person.profession, Physicist
Zhang Heng, people.person.places_lived, m.03lfd2q
Seismometer, user.avh.default_domain.ellerdale_topic.ellerdale_id, 0081-53a6
By 1892, they had developed the reliable horizontal pendulum seismograph., base.kwebbase.kwsentence.kwtopic, John Milne
Zhang Heng, people.person.profession, Astronomer
John Milne, people.person.profession, Geologist
Engineer, people.profession.people_with_this_profession, Thomas Lomar Gray
James Alfred Ewing, people.person.education, m.02wp11l
James Alfred Ewing, people.person.profession, Physicist
Luigi Palmieri, people.person.education, m.0sw314b
Luigi Palmieri, people.person.nationality, Italy
m.0qyz3p9, type.object.permission, m.019h
John Milne, base.kwebbase.kwtopic.assessment, John Milne was possibly the greatest individual contributor to observational earthquake investigations and the field of seismology.
Physicist, people.profession.people_with_this_profession, James Alfred Ewing
Earthquakes and Other Earth Movements, book.written_work.author, John Milne
The volcanoes of Japan...pt.1, book.written_work.author, John Milne
Politician, people.profession.people_with_this_profession, Zhang Heng
John Milne, base.kwebbase.kwtopic.has_sentences, Later in 1873, he went to Canada, visiting  Newfoundland and Labrador to study the mineral resources there.
Zhang Heng, symbols.name_source.namesakes, 1802 Zhang Heng
Zhang Heng, people.deceased_person.date_of_death, 0139
John Milne, people.person.profession, Educator
A catalogue of destructive earthquakes, book.written_work.author, John Milne
Scientist, people.profession.people_with_this_profession, Zhang Heng
John Milne, book.author.works_written, The volcanoes of Japan...pt.1
Palmieri, symbols.namesake.named_after, Luigi Palmieri
m.02wmymg, education.education.student, Thomas Lomar Gray
John Milne, base.kwebbase.kwtopic.has_sentences, By 1892, they had developed the reliable horizontal pendulum seismograph.
John Milne, people.person.gender, Male
m.0svt0_7, education.education.student, John Milne
Ascension Parish Burial Ground, people.place_of_interment.interred_here, James Alfred Ewing
Eventually, the chain numbered forty observatories, carrying out continuous seismic surveillance in a global network., base.kwebbase.kwsentence.kwtopic, John Milne
Zhang Heng, people.person.date_of_birth, 0078
In Japan, he began a comprehensive study of volcanoes and earthquakes., base.kwebbase.kwsentence.kwtopic, John Milne
John Milne, base.kwebbase.kwtopic.has_sentences, In 1871, Milne made an expedition to the Vatnajokull seismically-active area in Iceland.
Luigi Palmieri, symbols.name_source.namesakes, Palmieri
Physicist, people.profession.people_with_this_profession, Luigi Palmieri
m.02wp11l, education.education.student, James Alfred Ewing
Thomas Lomar Gray, people.person.profession, Engineer
Zhang Heng, people.person.profession, Mechanical Engineer
Zhang Heng, people.person.places_lived, m.04q69wz
Writer, people.profession.people_with_this_profession, Zhang Heng
g.125_ppgnk, base.schemastaging.pronunciation.yomigana, じしんけい
John Milne, base.kwebbase.kwtopic.has_sentences, John Milne was possibly the greatest individual contributor to observational earthquake investigations and the field of seismology.
John Milne, people.person.date_of_birth, 1850-12-30
James Alfred Ewing, people.person.nationality, Scotland
In 1871, Milne made an expedition to the Vatnajokull seismically-active area in Iceland., base.kwebbase.kwsentence.kwtopic, John Milne
John Milne, base.kwebbase.kwtopic.has_sentences, Milne was able to detect different types of earthquake waves,  and estimate wave velocities.
Seismological Society of Japan, organization.organization.founders, John Milne
John Milne, people.person.nationality, United Kingdom
John Milne, people.person.places_lived, m.04hsl4n
m.0h1b8xr, dataworld.gardening_hint.last_referenced_by, OBS: Ocean Bottom Seismometer
Zhang Heng, people.person.religion, Taoism
John Milne, people.person.education, m.0svt0_7
James Alfred Ewing, people.person.date_of_birth, 1855-03-27

Answer: OBS: Ocean Bottom Seismometer
OSS: Ocean Subbottom Seismometer