I have previously posted this reply (to different questioners) on the 
ARSCLIB and the SAA mailing lists.

I have done surveys like this and bought a meter. With a three-axis 
meter no particular concerns are necessary. In general, I found the 
levels in most situations to be below what will damage tape. In the old 
days, CRT monitors were about the most sensitive devices we had.

10 mG or less for crt monitors was the goal.

This question was asked in a different form (what is the level that puts 
tapes at risk) on the ARSCLIB list.

I will repost my reply here:

The reference I have used for years is:

I bought a one-piece 3-axis meter for about $150 from these folks about 
a decade and a half ago.

This looks like a good choice at $150

XYZ Axis EMF Tester (Cat. #A194)

However, the unit I have I think goes out to higher harmonics which 
might be interesting with large three-phase power installations, so 
another choice on the same page for $269, but it may be overly sensitive 
and not be able to measure higher strength fields discussed in the paper.

3-Axis Backlight Gaussmeter (Cat. #A107)

For $300 it looks as if this might be closest to what I had and found 
most useful.

Switchable 1:3 Axis Gaussmeter (Cat. #A153)

Though for $200 you can get this:

Datalogging 3-Axis Gaussmeter w/ PC (Cat. #A494)



On 8/15/2016 12:25 PM, Ruede, Laura wrote:
> Hi -
> The Texas Christian University Library is looking to move some archival magnetic sound and video recordings to new areas in the library and our off-site facility not far away.  Before we do this, however, we need to be sure that electro-magnetic fields in those areas are not above tolerance, in order not to damage the recordings.  I have some information on acceptable levels for this sort of material, but we don't have a gauss meter or other measuring device, and no one on staff has the expertise to wield such a thing.  TCU Physical Plant doesn't have a device or the necessary expertise either.
> I have the idea that a gauss meter wouldn't be too expense to purchase, so we could do that if needed.  I thought I'd ask whether there's anyone reasonably local who would be able to help us further, or if not, if anyone can refer me elsewhere.  Thanks very much -
> Laura J. Ruede, MLS
> Van Cliburn Archivist
> TCU Box 298400
> Fort Worth, TX  76129
> 817-257-7774
Richard L. Hess                   email: [log in to unmask]
Aurora, Ontario, Canada                             647 479 2800
Quality tape transfers -- even from hard-to-play tapes.