When you do not use a Grind on Demand machine, the simplest way to dose the porta filter is by "volumetric dosing," i.e., fill the basket past its rim and shave off the excess using a flat surface, such as a straight knife or even the lid of the doser. For this to work properly, the average density of ground coffee in the basket has to be the same every time you dose.
This means, you have to pull the doser handle consistently, move the basket around to dose evenly and knock the porta filter, or don't knock the porta filter, the same way every time. If you pull the doser handle once every second, or once every two seconds, does not matter that much, provided you do it the same way every time. If you pull once every second, little coffee gets accumulated in the doser before it is dumped into the basket. That little coffee will not compress the coffee already in th basket all that much. However, if you wait for five seconds, more coffee gets accumulated, and that coffee weighs more and will compress the coffee below when it is dumped into the basket, thereby increasing the density of the coffee underneath. This has a huge effect on how much coffee the basket can hold when the excess is finally shaved off.
In our training program, people generally start with a variability of +/- 10% by weight in their "volumetric dosing." Towards the end of the program they can consistently dose to +/- 1%.
When dialing in a particular coffee or just to check myself from time-to-time, I tare the weight with my portafilter/basket on the scale and check my dosing. Other than that I eyeball every dose as I run the grinder/dose just enough for each double so there is never any leftover after dosing is complete. I might wear out the ON/OFF switch or start capacitor in my grinder prematurely, but it's no biggie because I'm not wasting coffee all the time.
At times when I have back-to-back drinks I may run the grinder enough to do 3-4 doubles. When doing this I have found myself not liking full pulls on the doser lever because I get 5,6,7 grams with each pull and usually overdose. That's the reason I like the start/stop method and thwhack the doser clean for each drink. I'm not a fan of dosers for any reason, but it is what it is and I make the best of it. Until I can afford a K30 or Nino I'll keep thwacking away on my dosered grinder.
I USE MY LOOKING BALLS SON