So we've got this custom product that includes a voltage-controlled amplifier.
VCA chips as used in ultrasound and so on have nice low noise at the highest gains, but at low gain they stink on ice. The same is true of all transconductance-based VCAs unless you use a zillion stages.
Sooo, we're faking it with a dpot, an op amp with a mux-controlled resistor ladder, and an LPC804 Cortex M0+.
The resistor ladder is made out of standard-value Susumu 25-ppm resistors, so it's better than the dpot except that the switchable gains aren't exactly powers of two.
The simple way of handling this is to have the thing self-calibrate. That could be done at power-up and the cal table kept in RAM, or at test time with the table in flash.
There's some lore on the net that having the firmware write to the MCU flash is a bad idea.