:: zener tempco DUPLO play pen ...

the picture depicts possible combinations of tempcos to create a zero resultant tempco (theoretically). X-axis total zener voltage, Y-axis tempco from PDF of NXP zener BZV55

update March 28th

i have decided to try something different from panasonic DZ2Jxxx series
3x 3.6v + 2x6.2v = 23.2v total. drift -0.3mV/K. the -0.3 would be left there to counter resistor element +ve drift. however that could only be determined inside a oven. (and so i have to make an oven someday ...)