What do you use for temporary fixing?

[Nanako]

By temporary, i mean a matter of seconds

I frequently seem to have cases where i'm planning to mount something, on a wall or ceiling
And thiis thing has premade screwholes

so i need to draw marks on the wall to know where to drill
but before even that, i need to put the object up and level it out with a spirit level so that the screwholes i'll mark will make it not be crooked. The absolute worst case was some cast iron shelf brackets i put up a fre months ago. Where i discovered that casting is an imperfect process and every one of them was subtly different in a way that made measuring drill spots in advance near impossible

And at these times, i really wish i had three hands
but i don't, and for some inexplicable reason i don't even have anyone in my life i can call to just hold something in place

surely there are mechanical ways of doing things though. Do you guys have any recommendations?
I'd love some kind of claw or pincer, on the end of a flexible hose/arm thing, that i can make rigid when its in the right place so it can hold a couple kilos of iron in the precise spot i need it to be, while i measure and mark and inspect

any thoughts on this front?

 

[Wayners]

Lay items on paper.
Mark holes.
Use low tack masking tape to fix paper to surface and drill through markings.

 

[foxhole]

I just use a tape measure .

 

[endecotp]

cast iron shelf brackets i put up a fre months ago. Where i discovered that casting is an imperfect process and every one of them was subtly different in a way that made measuring drill spots in advance near impossible

Fit one bracket.

Hold second bracket against wall, put spirit level across.

Move bracket until level.

Mark holes.

 

[big-all]

2 or three or 4inch nails hold bracket or baton in position thump nail in at two positions and when happy its level then nail every position
now the nails are just markers so when removing note the holes/dents or marks and highlight them with marker pen or pencil and iff required drill for plugs
on plastered walls 90% off the time 2 nails will hold a baton whilst you work

 

[GhostIntMachine]

It does depend on what you are trying to fix. @endecotp's approach is pretty much what I do for a 2-bracket shelf:

Fit one bracket.

Hold second bracket against wall, put spirit level across.

Move bracket until level.

Mark holes.

Go to a longer shelf with more brackets and you'd fix the end pair first, drop a piece of CLS or the like on top and then work to that fir the other brackets. For really heavy stuff (e.g. 150mm square angle plates onto resin anchors) I'll often fix a smaller temporary piece of timber, like a 3 x 2 or 4 x 2, to the wall, levelled up with the top of the temp timber lined up to the bottom of the thing I really want to go on the wall. It's a lot easier to level a batten than a 50 or 100kg lump of steel. Two or three 5 x 90s will hold several hundred kilograms of weight. The angle plate then gets rested on top of the temp timber, drilled, fixed, and when fully secured the temp timber can be removed and the fixing holes made good. Can be a useful technique if level is critical but the item you are fixing is awkwardly shaped or excessively heavy, like the aforementioned angle plates. You don't even have to drill, plug and screw - for lighter stuff a few oval nails or panel pins may suffice

 

[Nanako]

Lay items on paper.
Mark holes.
Use low tack masking tape to fix paper to surface and drill through markings.

this will work great for things that don't need to be level

but i need to use a spirit level on most things, and then doing it on paper on the floor doesnt make much sense

Like, picture this scenario: i had drawn a line on the wall where i wanted the