All probes have a limited life, about 18 months.

now I find out that there is a brand that has a strip
when the meter can't be calibrated you just pull out a little more of the strip,not sure if you cut off excess.

I wouldn't worry about the dif. in conversion, its available as a comparison chart

I have a millwalkii tri-meter, but the probe still only lasts so long,I'm on my second $85 probe,wish I would have known what I do now,next probe is a generic off the net for $35