I have mentioned this before.

My last fuel injection shop job was in about 1988. At that time most of the inline Fuel Injection Pumps were timed during rebuilding of the Pump by the Drip Method (also called flow timing).
Some other companies used a Dial Indicator or a Depth Micrometer to achieve the same thing.

In the shop I worked in we had a gravity feed setup to supply the pressure. I have seen a Pic of an old Mercedes Diesel using a similar setup.

When drip timing the pump on the Vehicle I move the Fuel Injection Pump just a hair and snug down one or more of the Nuts and then I start pumping on the Hand Primer. When you do that the Fuel Pressure Relief/Over Flow Valve holds back some pressure.

While you are pumping count the drips. By doing that the pressure should be somewhat even.

Besides the Gravity Feed Setup another way is to connect an Electric Fuel Pump to supply the pressure.

Before you start it there is no reference marks on the Block to Fuel Injection Pump Flange scribe one so that you can return to were you started and it also gives you something to look at to determine how much you rotated the Fuel Injection Pump.

If you are not getting the drips you want stop, loosen the Nuts and rotate the Fuel Injection pump another hair and repeat the previous instructions till you get your drips.

If the Fuel Injection Pump is on an running engine and you are re-timing it; it only takes tiny amount of rotation to correct that. From the threads I have read lots of people grab the IP and rotate it like 1/8 inch (when something like 1/32 was all that was needed). That puts them beyond the sweet spot.

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84 300D, 82 Volvo 244Gl Diesel