4.5 Digit Micro Ohm Meter PCB Design (Arduino + Nextion + Modbus)

Need design of a 4.5 digit Micro Ohm Meter using Arduino-based PCB, Nextion HMI (display only) and manual buttons. System must use 4-wire Kelvin measurement.

Measurement Ranges (Must Follow):
10A → 2000 µΩ (0.1 µΩ)
1A → 20 mΩ (1 µΩ)
0.1A → 200 mΩ (10 µΩ)
0.01A → 2000 mΩ (100 µΩ)
0.1A → 20 Ω (1 mΩ)
0.01A → 200 Ω (10 mΩ)
1 mA → 2000 Ω (100 mΩ)
0.1 mA → 20 kΩ (1 Ω)

Accuracy target: ±0.03% ± 4 digit

Controls:
6 Buttons:
Range Up, Range Down, Save/Recall, Trigger, Pulse, Test
HMI (Nextion):
Display only (no control)
Show value + range + status
Provide variable names & page mapping (HMI design not required)
Other Requirements:
Modbus RTU communication
Range display on HMI
Internal hidden potentiometer for calibration
Stable, low-noise design
Deliverables:
Schematic
PCB files (Gerber + source)
BOM
Arduino code
Modbus register map
Basic calibration guidance