Metering through the filter, especially with orange and red, are usually not accurate. Here is what Ilford says on their website:(posted 8239 days ago)"Cameras with through-the-lens metering will usually adjust the exposure automatically when using filters. With some automatic exposure cameras, the correction given for deep red and orange filters can produce negatives under exposed by as much as 1 1/2 stops."
The best way to compensate for filters in B&W photography is to meter without the filter and then manually apply a filter factor. The filter factor should be calculated based on tests you conduct that take into account your film and geographic conditions. In areas of high altitude and/or intense sunlight, larger filter factors are often required. Filter factors are usually less for cloudy days, locations with high humidity, and tungsten lighting. You also need to take into account how much shadow detail you need in a particular image, because there is more blue light in the shadows than in objects reflecting direct sunlight (orange and red are "minus-blue" filters).
If you are using orange or red filters with Tmax-100 film, there are additional issues you will encounter that will require that individual testing be conducted to come up with your own filter factors.