The Institut de Physique du Globe in Paris (IPGP) has a solid tradition in long-period seismology and instrumentation. The IPGP Seismological Laboratory designed handmade instruments from 1952 to 1982, mainly to study the Earth tide tilt. After several attempts, the first prototype of a tiltmeter was constructed in 1957 by P.A. Blum (Blum and Jobert 1959; Blum et al. 1964). This sensor was a horizontal mechanical seismograph with classical Zöllner suspension (Zöllner 1869), made of fused silica working under vacuum (Figure 1A). Optical amplification and photographic recording at a velocity of 1 cm/h...

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