An apparatus, comprising: - a process tunnel, extending in a longitudinal direction and bounded by at least a first and a second wall (120, 130), said walls being mutually parallel and spaced apart so as to allow a substantially flat substrate, oriented parallel to the walls, to be accommodated there between, and - a plurality of gas injection channels (122, 132), provided in both the first and the second walls, wherein the gas injection channels in the first wall are configured to provide for a first gas bearing, while the gas injection channels in the second wall are configured to provide for a second gas bearing, said gas bearings being configured to floatingly support and accommodate said substrate there between, characterized in that - the first and/or second walls (120, 130) of the process tunnel are fitted with at least one substrate detection sensor (S') at a respective substrate detection sensor location, said substrate detection sensor being configured to generate a reference signal reflecting a presence of a substrate between said first and second walls near and/or at said substrate detection sensor location, wherein the at least one substrate detection sensor includes a pressure sensor (S' 1,2) configured to register a gas pressure of the first and/or second gas bearing; and in that the apparatus further comprises: - a monitoring and control unit that is operably connected to the at least one substrate detection sensor (S'), and that is configured to record said reference signal as a function of time and to process said reference signal, wherein a pressure-time registration of a passing substrate includes a peak with a leading flank and a trailing flank that hold information about the shape, orientation and/or speed of the substrate, wherein the processing of the reference signal includes at least one of: ∘ displaying information encoded in the reference signals for inspection by an operator; and ∘ automated analysis during which the reference signals are analyzed to determine one or more substrate properties reflected by the reference signals and related to the lateral position and/or longitudinal position of a single substrate or multiple substrates. - a process tunnel, extending in a longitudinal direction and bounded by at least a first and a second wall (120, 130), said walls being mutually parallel and spaced apart so as to allow a substantially flat substrate, oriented parallel to the walls, to be accommodated there between, and - a plurality of gas injection channels (122, 132), provided in both the first and the second walls, wherein the gas injection channels in the first wall are configured to provide for a first gas bearing, while the gas injection channels in the second wall are configured to provide for a second gas bearing, said gas bearings being configured to floatingly support and accommodate said substrate there between, - the first and/or second walls (120, 130) of the process tunnel are fitted with at least one substrate detection sensor (S') at a respective substrate detection sensor location, said substrate detection sensor being configured to generate a reference signal reflecting a presence of a substrate between said first and second walls near and/or at said substrate detection sensor location, wherein the at least one substrate detection sensor includes a pressure sensor (S' 1,2) configured to register a gas pressure of the first and/or second gas bearing; - a monitoring and control unit that is operably connected to the at least one substrate detection sensor (S'), and that is configured to record said reference signal as a function of time and to process said reference signal, wherein a pressure-time registration of a passing substrate includes a peak with a leading flank and a trailing flank that hold information about the shape, orientation and/or speed of the substrate, wherein the processing of the reference signal includes at least one of: ∘ displaying information encoded in the reference signals for inspection by an operator; and ∘ automated analysis during which the reference signals are analyzed to determine one or more substrate properties reflected by the reference signals and related to the lateral position and/or longitudinal position of a single substrate or multiple substrates. ∘ displaying information encoded in the reference signals for inspection by an operator; and ∘ automated analysis during which the reference signals are analyzed to determine one or more substrate properties reflected by the reference signals and related to the lateral position and/or longitudinal position of a single substrate or multiple substrates.