Is this a big deal? I noticed, when the dial is at below 50%, the display show about 5 % less. But when the dial is at 50%, the display show higher than the dial's and as I turn the dial to higher, the difference can be as high as 20. It matched at 100% though. I have been noticing this for a while but just ignored it until now, me 2 yrs old T-cell-15 starts making less and less chlorine with no fault indicators. All my chemical reading are fine, including combined chlorine. All previous cells lasted 3.5 yrs.
My board is 12 yrs old though and went through some repairs but working fine.