The razor tool is a very good idea on the Barista Express so is very likely to be on the DTP. The height of the dose of grinds does matter. The grinds expand when the water goes in so too high is a very bad idea unless it's being done within limits on purpose. Too low has other problems usually relating to rather soggy pucks.
The razor tool on the DB is the pits and doesn't work out well at all.
While it's a pain home espresso machines need certain steps to be taken to get consistent results. One of those is a consistent weight of grinds. The other from that is consistent shot time and output. The razor tool can give a ball park weight. Handy when the grinder setting is being changed as finer grinds take up less space so usually need and increase in the weight used.
Best simple option on tamping is as hard as you can manage and keeping it level. If out it's possible to correct tamps but not and ideal thing to do just a better option than leaving it well out of square.
So scales are needed. A good option is 1kg ones that read to 0..1g. Not too small as ideally they need to be able to weigh the entire portafilter balanced on them to check the weight of grinds that is in it. Mine have 130mm dia platform which is fine for that and if I move the portafilter around on them a bit the weight doesn't change. 100mm square is probably ok. One idea of the razor tool is to avoid weighing the grinds - always put a bit to much in and razor off excess.
Still need scales though really. So the first thing to do is to adjust the grinder to give some ratio of grinds in to weight of the shot that comes out within a certain time. One that gets mentioned a lot is 30 secs and 1 in to 2 out. A ratio of 2. Also that a single is either 25 or 30ml and a double 50 or 60. 1ml weighs 1g so weight can be used to check that if needed. It's more than accurate enough. Later some one might want to taste other ratios. Usually for home use those might range from 1.5 to 3 shot sizes varying accordingly still at 30sec or even that could be adjusted. Eg the 1.5 ratio might be best obtained by reducing time and the amount out. The high ratio by grinding for it and keeping time the same. The idea is to get a taste that the drinker likes and varying this aspect will alter taste. Commercially speaking ratios may go well over 4.
Every time the grinder setting has been changed the previous setting's grinds must be got out of the grinder and thrown away. 2 secs is likely to do that on most of them. The Sage grinders don't retain much actually but if they aren't got rid of it will mess tuning up. On those I always finish up an adjustment by going finer to take out any play even when I make a coarser adjustment. When setting finer one mark of adjustment seems to be ok, if more than that run the grinder while making the adjustment. Some makers will state that the grinder should be running when ever an adjustment is made. The danger is going finer though - using the adjustment to crush the grinds from the last setting.
The last aspect is that small adjustments can be made by altering the dose of the grinds that go in. Less will increase it and more will decrease output. Too low tends to leave a messy puck that may not extract consistently and too high can reduce extraction resulting in coffee that is weaker than it could be because a coarser grind needs to be used to get a ratio. Taste will change as well. One guide I used a lot on the single basket on the BE was very slight signs of the hole in the screw that hold the shower screen in place on the puck. It's fiddly finding it, increase the dose in steps of say 0.2g until it appears and then back off to see if it goes, use it there or go back up again. Sometimes the puck stuck, another 0.2g fixed that. If very distinct signs of the hole can be seen on the puck there is very probably too much in.
John
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