You don't measure the coolant that way. That is what a coolant refractometer is for.
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The calipers are electronic. They are sealed and ip rated.
I work as a cnc machinist. Coolant is mixed between 3 and 10% concentration cutting oil to water or what I run these days is ~90 weight viscosity cutting oil called ilocut 5720. I run through lots of nitrile gloves that are always oily trying to measure parts.
The calipers are ip67 and micrometers are ip65.
6x meaning is
No ingress of dust; complete protection against contact (dust-tight). A vacuum must be applied. Test duration of up to 8 hours based on airflow.
X7 meaning is
Ingress of water in harmful quantity shall not be possible when the enclosure is immersed in water under defined conditions of pressure and time (up to 1 meter (3 ft 3 in) of submersion).
Test duration: 30 minutes.
Tested with the lowest point of the enclosure 1,000 mm (39 in) below the surface of the water, or the highest point 150 mm (5.9 in) below the surface, whichever is deeper.
X5 is
Water projected by a nozzle (6.3 mm (0.25 in)) against enclosure from any direction shall have no harmful effects.Test duration: 1 minute per square meter for at least 3 minutes
Water volume: 12.5 litres per minute Pressure: 30 kPa (4.4 psi) at distance of 3 meters (9.8 ft)
In other words if I ran the ones that OP bought, they'd be destroyed in a very short time.