Raytheon ST-60 instruments
We have used ST-50 for the last 9 yrs. and still are dry, despite longly exposed.
As far as I understand, main differences between 50 & 60 are more related to the display and numbers size than to software or hardware stuff.
However I did found that quartz display, even if properly covered, tend to difuse and to loose clearness, brightnes and clarity over time. Is quite difficult to find a replacement for theses displays.