Severn公司是为美国海军船舶局开发和制造弱磁材料磁导率的目的的试验仪器工厂。在朝鲜战争期间，它被用于扫雷计划。格罗斯先生和Ellinghausen作为美国海程实验站的平民（后来的戴维W.泰勒研究实验室）在马里兰州安纳波利斯。他们的研究领域是弱磁性不锈钢磁导率。
The Low Mu Permeability Indicator is a simple, rugged, non-destructive inspection instrument developed for laboratory, shop and field use. The GO, NO-GO feature permits instant acceptance testing of austenitic stainless and Manganese steel base and weld materials. The Indicator requires no external standards, no adjustments, no visual readings and is unaffected by position. It performs equally well on sheets, plates, rods, irregular shaped objects and individual parts of complex components. It is effective in locating areas of high or low permeability in heterogeneous products and has application where cold forming and annealing operations are required.
弱磁导率计是一个简单的，坚固的，为实验室开发的无损检测仪器，同时适合车间和现场使用。合格、不合格功能允许即时的验收测试的奥氏体不锈钢、锰钢基和焊接材料。指示不需要外部的标准，无需调整，没有视觉的读数。它执行同样的标准检测板，棒等不规则形状的物体和复杂零件的各个部分。它是有效的定位领域的高或低磁导率的异质产品和应用在冷成形和退火操作要求。
The Indicator weighs 3 oz. and is 5 inches long making it comfortable for hand held operations. All metal components are bright Nickel plated. The Indicator and it's Inserts are furnished in a handsome wooden box. The Indicator conforms to SEV-ENG-96001, the replacement specification for MIL-I-17214B.
指示器重3盎司，5英寸长的很舒服的手持操作。所有的金属部件都镀亮镍。指示器和它的插入件都装在一个生产商提供的非常漂亮的木箱内。这个磁导率计符合标准sev-eng-96001，MIL-I-17214B。
The Indicator is available with any combination of Inserts. Available Insert values are:
该磁导率计可以插入任意组合，允许插入值包括如下：
1.01 Mu | 1.02 Mu | 1.03 Mu | 1.04 Mu |
1.05 Mu | 1.06 Mu | 1.08 Mu | 1.09 Mu |
1.10 Mu | 1.15 Mu | 1.20 Mu | 1.30 Mu |
1.40 Mu | 1.50 Mu | 1.60 Mu | 1.80 Mu |
1.90 Mu | 2.00 Mu | 2.20 Mu | 2.50 Mu |
3.00 Mu | 3.50 Mu | 4.00 Mu | 4.50 Mu |
5.00 Mu | 5.50 Mu | 6.00 Mu |
