Originally Posted by jernejk
As I remember the Zone System, yes, the idea is that 18% gray card is 18% gray print. The gray card and the Zone V print are the pivots point around which the system revolves, so to speak. All else being equal, having the card be brighter points to overdevelopment, raising that value into the next zone. Then again, your meter could be set for a different gray value than 18%, leading you to overexpose (meaning that you have raised zone 0 to zone 1, and all the others will go up
But, always the but- there are a variety of issues at play. For example, the color sensitivity of the film and the light will affect how certain shades are reproduced. Filters on the lens will also change the rendering of different colors. Paper development and exposure has its own 'zone system' at work, and you can introduce variations there.
In the end, if the print looks like what you want it to look like, you did right. All of these techniques are tools, not religions. If it gives you the control and understanding you want, keep going.