Rock-Cut tomb locating using Magna-Trak 200

[gooch]

Hi Guys
I recently purchased a Magna-Trak 200 Magnetometer and was hoping one of the Geo-Fizz guys can help me with some of my questions.
I'm interested in using this hand held device for the location of Rock cut Tombs, I specifally bought this model as it has a digital reading from 0-99, I have read that mags are used for there ability to map anomalies in the soil structure etc stone walls and highly magnetised soil, as I dont have access to archaeological type of magnetometer that can plot the readings on to a laptop and produce an image, I was hoping to try a basic test with my magna-trak, which I did the other day.
I tried the machine out on a roman and Greek necropolis which has around 20 rock cut tombs that have been opened over the years, some filled back in, I set the machine to 50% of its sensitivity and set out to note the readings of the mag at the left side of the tomb which was solid rock then moved to the centre over the cut out part which would be where the entrance to the Tomb is and the filled in soil which is around 2 meters deep, then moved across to the right to solid rock again, I noted that there was a difference in the readings between the solid rock and the entrance soft soil But was hoping someone would help me out with some tips in taking these readings and the best possible method I could use in pinpointing the the actual cut in the rock. I also used the same method as above but this time I tried the mag over the centre of the Tomb which would be a hollow void and No soil just Rock and again noticed a difference in readings.
I would be most gratefull if someone would shed some light on this for me and the best way to use this particular machine for my intended purpose.
Look forward to your replies.
Thanks

[cptbild]

A Magnetometer !
Is just That!
A Magnet Meter !
It measures ONLY! Magnetic Fields
AND!
Alerts to the presence FERROUS metals, in that field, by way of thier shifting of that field
Not to other metals
Not to any Voids
Sorry!