132 of the strain gauge 131.

The measuring module 13 thus provides data making it possible to compare the spreading of different coatings. Indeed, the testing of the different coatings consists of spreading, on a reference surface, an identical quantity of coating. This test makes it possible, for each coating, to recover data. These data are in particular data relating to the force exerted on the trowel by the user. These data relating to strain are performed temporally. It is thus understood that the measurements taken by the strain gauges 131 are carried out at regular intervals. This makes it possible to track changes in the strain applied by the user on the trowel during the step of spreading the coating. Force curves are obtained as a function of time, such as those illustrated in FIG. 13. These curves C are thus studied to determine which coating is the easiest to spread.

Studying these curves C shows several characteristics of the spreading step. Indeed, it is possible to extract data regarding the maximum force of the peak, the average force of the plate, the duration of the gesture, the jerkiness, the number of gestures (=number of peaks) per m2 covered, the number of gestures per minute.

Indeed, it is considered that all these quantities can represent the force that the applicator must apply in order to spread the coating, the mortar.

For example, the number of peaks corresponds to the number of gestures necessary to spread the coating. It is assumed that a large number of gestures means that the coating is more difficult to spread because it requires more gestures.

On the other hand, it is assumed that the number of gestures per minute is indicative of a capacity, of an ease of the coating E to be spread. Indeed, a coating E that is difficult to spread requires, with equal force, a duration to be spread that is greater. Consequently, if the measuring module 13 detects a greater number of movements, then this means that the user more easily spreads the coating. This item of data relative to the number of gestures per minute is to approximate the item of data concerning the duration of the peaks. Indeed, if the duration of the peaks is long, this may mean that the number of peaks per minute will decrease, which means that the coating E is more difficult to spread. This may also mean that the movements of the user are wide therefore much more surface is coated with a single gesture. But this may also mean that the movement is slow and therefore that the operation consisting of spreading the coating is more difficult. Combining with speed or acceleration information can make it possible to understand better.

Regarding the maximum force of the peak, the average force of the plate and the jerkiness, that is the slope of the force of each peak, these data can also be interpreted to enable an analysis of the coating E and its capacity to be spread. Indeed, the data on the measured maximum or average force makes it possible to determine the capacity of the coating to be spread. The higher the average or maximum force, the more difficult the coating is to spread because it requires a greater force to be spread.

As regards the stroke corresponding to the slope of the force as a function of time of each peak, this value also makes it possible to assess the ability of the coating to be spread. Indeed, it is assumed that the less capacity a coating E has to be spread, the smaller the slope. This is due to the viscosity of the coating E that will be lower and which therefore has a greater resistance to spreading.

It is also possible to approximate the amount of energy expended by the operator. This energy is approximated using the following formula:

W
i

=

∫

F
i

⁢

dl

=

∫

F
i

(

dl
dt

⁢
dt

)

=

V
gesture

⁢

∫

F
i

⁢

dt

Where dl=distance from where the gesture i is applied

The result is:

W
total

=

∑
i

W
i

These data can be analyzed by the user or by computer in order to compare the data for each coating and to determine the coating that appears to be the easiest to spread.

FIG. 14a shows curves of the force as a function of time for four coatings A, B, C (standard coating) and D. FIG. 14b illustrates the mean forces calculated for each coating. This makes it possible to observe that the standard coating C is that which has the highest average force, so it requires more force to be spread. Furthermore, it is noted that the coating C requires a longer spreading step (80 seconds vs. 70 seconds or less for the coatings A, B and D).

Though these data make it possible to compare the coatings, it is possible to use them for other applications.

A second possible application is the use of these data of maximum force, average force, and number of gestures per minute to compare the surfaces to be coated. This is because although these data can be used to compare different coatings on a reference surface, the inverse consisting of comparing different surfaces to be coated with a reference coating E is possible. This possibility comes from the fact that each material used as a substrate on which a coating E is spread has its own surface characteristics, in particular the surface state characteristics.

In this case, the use of the data is similar since the greater the force needed to spread the coating, the less conducive the surface is to the spreading of a coating E.

It is also possible to make multiple comparisons associating different mortars and different surfaces or substrates. FIG. 16 thus shows the energy expended by an operator for different mortars for different surfaces. In this FIG. 16, it can be seen that mortar M3, for each of the surfaces S1, S2, S3, requires more energy to be spread than mortar M2, which in turn requires more energy than mortar M1. Furthermore, looking at mortar M2, it is possible to note that surface S3 requires more energy than surface S2, which in turn requires more energy than surface S1.

Another application consists of using the instrument