I have to disagree with the audio modulation,the 705 does have this ,where as the 305,505 doesn't
(I spoke to Minelab about this)
anyway with my 705 I can get a faint audio meaning deep ,and it certainly is deep,
other targets are so deep the machine hasn't got ''the trousers'' to push the headphone speakers
these are my favorite ones,after digging and then going over the ''post hole'' because of the effect of
the sweep being a kind of ''in air '' >>>>one even if you had firstly got the faintest whisper (audio modulation)

you now have only the display,these take a fraction of power to work.
Now the exciting part, the pin point probe when put into the bottom of the chasm will now sound out if there is anything metalic
as it is a miniature detector scanning near to the ground.
So to conclude
the audio will be fainter the deeper the target,
the display will still be true after the audio has gone,
if the ground is ''fluffy'' aerated ,then tiny air pockets between the soil particles will effect depth,
Different coils i.e concentric or DD will see the target and search differently.
The old saying ''you have to go over it to find it'' stands true.
Hand on heart ,iv'e found many small coins (25 mm diameter) at depths up to 16/18 inches,and assemblages of coins at over 24 inches
i have a folding rule,and usually measure the depth,these are in ground recoverd finds,not fall backs where by the target falls deeper the more you dig,
best regards,
the 705 is by far the best machine iv'e owned in over 30 years of involvment in the hobby.
Oh nearly forgot,
if you look at my avatar,i'm actually stood in one of my dig outs
