Hi there,
RF Explorer internal frequency is correct in range of +/-2Khz if calibrated. The reason you may see up to 5MHz deviation is not due to frequency accuracy, but screen resolution. To understand how the screen becomes a limitation in your measurement is important to get the best out of the instrument:
RF Explorer has 112 pixels to represent horizontal spectrum. Therefore, if you select a frequency span of, say, 1MHz, you get 1,000KHz/112=8.9KHz resolution per screen point. If you select a frequency span of 100MHz the resolution now becomes 100,0000KHz/112=892KHz, etc.
For best results in normal operation, you should use a large span to start, say 30MHz in the picture above, to locate point of interests. Then move to narrow span to get higher resolution frequency read.
If you need to read frequency with higher resolution, click ENTER once to enter Advanced Mode, then use RIGHT key to reduce span and, therefore, increase resolution. Or use FREQUENCY MENU to select a new center frequency of your choice, and a smaller span value.
It also becomes very useful to pre-record your frequencies of interest with large and narrow spans, using Presets, so a single click can help you navigate through your frequencies of interest using high and low resolution as needed. For more details www.rf-explorer.com/preset
Hope this helps