We're encountering an issue with our test system where we divide a fixed total flow between various MFC's that have different max flow capabilities. The total flow often shows small, but noticeable errors that are degrading our experimental data.

I finally tracked the problem down to the fact that _set_setpoint() in serial.py only sets the setpoint to two decimal places of precision. Our flow rates are getting rounded up by this function. e.g. 0.376 SLPM is being set as 0.38 SLPM. This flow controller is a 1 SLPM max flow device, so the code is artificially limiting its precision to 1 part in 100, whereas the actual nominal capability is 1 part in 64,000. The driver is effectively degrading the precision of the device.

To my mind, this is clearly a bug.

In the documentation, I see that the serial protocol of these MFC's allows for the setpoint to be configured as an integer between one and 64000. So I can work around the problem by writing my own version of set_flow_rate(), but it's really frustrating that the standard API doesn't provide a way to access this capability.