I cannot fathom why cheap chronoscopes keep getting used?, buy some Skans and put them in a wooden frame to keep the rifle in line, as used to be the case, they worked well until they where left out in the rain
Whats it been 3 or 4 years of buying cheepo chronos?.
But ultimately, what ever gets used needs to be cared for, ie, keep it undercover, away from direct sunlight, frost and water.
PS, and dont buy second hand
PPS, you Do not require a calibration certificate within the first year of life.
PPPS, Scans are self checking/calibrating