Strange VID on F75

Hi,
Last time when i use my F75 i see strange VID on the screen - there is no numbers on LCD but only + (plus) indicator.
I wored in AMM and dig deep hole (yellow sand-inside land-GB about 68-75) about 30-32 inches (when i get shallow targets i have more and more signals from iron little pieces-too bad i don't find nothing special).

Have anyone that VID ??
Is this mineralization or ground signal ??

PS.Sorry about my english

Hmmmmmm. Usually corroded 'steel' items will cause this. Rusted iron can also cause this...... but it is usually steel (iron w/alloys added). These targets are difficult to pinpoint.....and will usually pinpoint towards the edge of the coil (not the center).