You cannot be serious. If you are they need to be new bubbles, You can purchase new bubbles, Just ask at any hardware store.

You only read one vial, depending on whether you are trying to level horizonally or vertically. Some tools also have a vial for 45-degree leveling.

The air bubble inside the vial will be perfectly centered between two lines when the tool is level for the given orientation.

Hold the tool horizontally level — one of the vials in the center is usually oriented parallel to the tool and will tell you if it is perfectly level.

If you hold the tool vertically level, one (maybe both) of the vials at the ends will tell you if you are tilted slightly to the left or right.

Place the tool on the sill of the new window, or hold it vertically against a jamb and read the proper vial.

Many levels have a straight (in line with the level) glass tube with liquid in it. There should be two lines on the glass. When you have it level, the bubble of liquid is between the lines. You may also have a glass vial that is on an angle (45 degrees) for establishing that angle. The vials on the ends should go across the width of the level and are used to “plumb” the edges of surfaces that are vertical.

Windows for new construction have a nailing fin, and are installed from the out side of the house. You can use a replacement window (fits in a window opening from the inside), but you will need to do all the trim work. Figure out the cheapest way. You can also buy new construction windows, cheaper than $300.
Builder for 40 years.

An insert is usually made to very specific dimensions and use your existing window frame as apposed to removing the old window frame and all and replacing it completely. If you are confident in your abilities inserts can save you a lot of money.

the bubble lets you know if it’s level or not. When it’s in the center, then it’s level

That is cheap. On most convertable tops, the back window is not serviceable and the entire convertable top must be replaced.

The bubbles should be in the center of the vial (between the lines). The long side of the level is for horizontal position, the end is for vertical position. So, for the horizontal position, you put the level long ways, for the vertical position, you put the level up and down.

There is no need to have the old siding removed. The new siding can be installed over the old. This is one way to save money. As for the cost of the siding and windows, it really depends on the brand you choose and the contractor who installs it. We had 11 Harvey windows and Certainceed siding installed (sp?) and the whole job cost us 13,000 dollars. Good luck and do your homework before choosing a contractor for the job.

we always used a water level or a construction lazer level. to find the lowest corner of the building and start there by nailing the starter strip as high up as the nailer would allow, then keep it level all the way around,
unless the building is way out of level. you should wind up ok on the high side