The Silver [size=small]micro[/size]MAX [size=small](for those who don't know, it is labeled µMAX using the 'micro' symbol, not the letter 'u')[/size] is a silent-search, motion-based detector that lacks a true, conventional, Threshold-based All Metal mode. The "All Metal" selector switch action simply changes to what should be a non-adjustable All Metal Accept, or close to Zero Disc. setting. Thus it will respond to all metal objects, ferrous or non-ferrous.
The variably adjusted Discriminate mode uses the ED-120 Disc. circuitry which means at the minimum Disc. setting it will accept the upper 120° of the 180° of the detectable target range. Thus, iron nails and almost all ferrous targets will be rejected at the minimum setting. All Metal mode can be used to find more targets, including iron, and possibly assist a little with Pinpointing, but not like a true Threshold-based All Metal mode can.
In theory, the Discriminate control should be bypassed once you select the All Metal option with the toggle switch. However, as we have seen with some former Tesoro models [size=small](such s the Sidewinder microMAX and original Conquistador, to name only two)[/size] there could be a glitch in the circuitry design whereby the Disc. control can also shift the Ground Balance.
IF there is any increase in 'air test depth' with the Disc. control adjusted from minimum to maximum when toggled into the 'All Metal' function, then it would suggest the GB has been shifted more negatively than what the preset reference is. If that is the case, I would suspect the GB shift could be too negative for reliable performance in any higher mineralized environment in that search mode, or possibly even cause falsing and poor performance when in even mild-to-moderate ground mineral conditions.
My personal opinion is that the Disc. level control be left where it was during searching when you opt for the All Metal function. I can't check it out because I don't care for the Silver µMAX and therefore don't have one in my detector battery. However, out of curiosity, when I get my hands on one of those models I'll check it out.
Monte