Here is a Zone System sticker for the L-758DR:
Zone Sticker for L-758DR
Print it out on sticker paper. Put sticker centered on the bottom border of the LCD panel. Cover the panel and sticker with a "cellphone" type screen protector.
1. Set meter to daylight [T] (shutter priority) mode. So f/stops display on bottom scale.
2. Set meter to spotmeter mode.
3. Take a single spot meter reading, for example take a shadow spotmeter reading.
4. The arrow points move around with the meter reading. You can change shutter speed display on the meter and the arrow points will move.
The sticker is a reminder of which Zones go with the arrow points. In the picture example, to place the shadow reading on Zone II, use f/45.
5. Take additional single spotmeter readings but do not use memory. If the same f/stop "falls" on the Zone you want that spot in every case, then you have a negative to develop to "N". If all the readings are close together, then you probably have "N+1".
The weakness of this idea: I can't directly get N+ and N- values.