record(ao, "$(P)A") {
    info(Q:group, {
        "$(P)":{
            "A":{+channel:"VAL", +putorder:0}
        }
    })
}

record(ao, "$(P)B") {
    field(FLNK, "$(P)SUM")
    info(Q:group, {
        "$(P)":{
            "B":{+channel:"VAL", +putorder:1}
        }
    })
}

record(ao, "$(P)C") {
    info(Q:group, {
        "$(P)":{
            "C":{+channel:"VAL"} # omit +putorder to prevent write
        }
    })
}

record(calc, "$(P)SUM") {
    field(INPA, "$(P)A NPP MSS")
    field(INPB, "$(P)B NPP MSS")
    field(INPC, "$(P)C NPP MSS")
    field(CALC, "A+B+C")
    info(Q:group, {
        "$(P)":{
            "SUM":{
                +channel:"VAL",
                +putorder:2,
                +trigger:"*"
            }
        }
    })
}