Double Plus or Minus Tolerances
This may or may not be the correct place to ask tnis question but here goes. The company I work for is manufacturing rplacement and repair parts for aircraft made in Israel. Some of the drawings are in metric and some are in SAE and some have a combination of both. I am a machinist not an engineer so please forgive me if I use the incorrect terms for my descriptions. Some of the metric drawings use a double minus (-.027mm,-.034mm) tolerance or a double plus (+.027mm,+.034mm) tolerance. Based on my experience this would be interpreted as the nominal diemenision (theoretical desired size) with a unilateral tolerance of -.027mm, -.034mm. I have been told this is not correct and they have no evidence to back this up except there past experience. I was told this is a european tolerancing method. but can not fine the needed standard for this method. this is the way it was explained to me I just need some hard evidence to back this up.
8.00mm nominal size
tolerance on drawing -.027mm,-.034mm
8.00mm-.027mm = 7.973 actual desired size
8.00mm-.034mm = 7.966 minum actual desired size
total unilateral tolerance = -.007mm
Is this correct? What drawing standard is this covered by?
Thank you in advance for any and all help. If I need to provide a better example please let me know.