I have just finished my OZ2CPu wattmeter,

The uncalibrated signal response is: +1/-1 dB from 1MHz to 450MHz. Input SWR will varry from 1.00 to 1.30, depending on input frequency. To make the SWR good, you need to assemble the input circuit correct and adjust the capacitor.
Input power range: -60 to +30dBm that is 1 nW to 1 Watt.
This instrument can be used and calibrated from 1 kHz and up to 500 MHz. It is possible to measure power relative all the way up to 900Mhz. A software routine can calibrate the 0dBm point at 5 different frequencies to make this instrument accurate within 0.5dBm !! The calibration data is stored in EEPROM so the instrument will remember all, also without power.
At frequencies above 300Mhz this instrument should not exceed inputs over +20dBm (100mW) to keep the good accuacy.

I have recalibrated this device on following frequency, 3, 15, 30Mhz HF, 145Mhz VHF, and 432Mhz UHF , only 5 points are available, the author don’t want and will never add more. sadly.