Some more photos of boxed Clone PI AVR metal detector and self made coil. I have made a coil from Ethernet cable between two round plywood sheets filled with Makroflex sealant. More about making coil from Ethernet cable can be fount here. Idea how to seal everything came from here. Clone PI AVR intself was boxed in a box I bought in local electronics store. I decided to add a switch to switch off external beeper so that sound will be provided only through headphone socket. For the coil connector I have selected some two pin microphone connector. I think in general it came up pretty well. Will be mounting everything on appropriately bent and painted PVC pipe. Will post pictures later. Some day. Probably.
If you want to zero for 50-200 meters at 10 meters and save some walking just use this ballistic calculator to get bullet drop at 10 meters with your bullet and location data (provide that zero is at 50m). Then put two dots on target, one on the middle, another below at distance you have calculated for bullet drop for 10 meters. From 10 meters aim at the upper point and adjust optics so it would hit at lower. Done. For my location and bullet, I get 3.46 cm bullet drop for 10 meters distance.